# Digital Coax>D/A_A/D_D/A - Amplifiers



## ncv6coupe (Oct 25, 2009)

Didn't want to call out brands but say a zapco dc system vs a regular "properly shielded" rca cable system in terms of signal degradation when we are forced to use multiple processors like the ms-8 along with an aftermarket head unit. Can some of you really hear that extra conversion as a dump to the hi-fidelity playback of your systems?


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## Sarthos (Oct 29, 2010)

I'm not familiar with the zapco system. I do know that with digital cables you do get less interference in the signal going to your amps.


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## Cancerkazoo (Jul 21, 2006)

I've never used digital line level wires, but I can say if you have no grounding issues i don't think it is needed. Back in the day (when IASCA had a 0-50 watt class) I damaged my RCAs and bought cheap unshielded $3 a pair ones from a grocery store and still got a 10 in the no background noise section. ( I forget what they called it)


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## azngotskills (Feb 24, 2006)

Zapco uses "balanced" symbilink cables not digital, if you are talking about digital signals you would be referring to optical or digital coaxial. Just wanted to make sure you knew what you were talking about.


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## ncv6coupe (Oct 25, 2009)

^^yeah I wasn't clear about the oddball zapco hookup along with the digital seperately. So we have symbilink vs good or even cheap rca's vs riding the light/digital. I myself prefer balanced lines either by transformer after head unit or amplifier input. That's all the noise reduction steps I utilize in my signal chain and fuzziness is inaudible to me.


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## Genxx (Mar 18, 2007)

Zapco is just a proprietary balanced analog system. Nothing odd-ball about it. So I am not sure what you are referring to.


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## ncv6coupe (Oct 25, 2009)

The din setup, nothing oddball about balanced lines, just about the expensive cables you need for the complete line driver setup. I'm surprised the digital guys are tight lipped about this question? I've heard different systems running digital 701's and even analog (insert every popular processor here) and they have both had great resolution so why so quiet about the supposed superiority of full on digital? Did I just choose a fragile topic to debunk? oke:


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## Genxx (Mar 18, 2007)

Long ago there is a thread about cables that people have used that are as cheap as buying RCAs that work with the Zapco amps.

There are many threads that have discussed the issues with noise from running RCA to the H701. It is hit or miss with the H701 if you will have noise or not. No one has ever reported issues with running digital to H701. This topic has been discussed on here and else where many many times.

So really you just discussing stuff that has been discussed many times on this forum and on the web.


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## ncv6coupe (Oct 25, 2009)

That's why I first mentioned that I didn't want to get into brand name calling. I'm not talking about noise only, my main focus is on the virtual resolution and crispness of the sound. My point was some people are full of **** and feel like they have golden ears to be able to distinguish between any modern dac in the mid-high end equipment market if they had to convert it to process it 2 times via rca's vs 1 time via optical/coax. I see this is why no one wants to step into the flame willingly. I daisy chain 2 processors via rca to get all the channels I need for my setup. It sounds just as detailed and crisp as the best that I've heard as recent as meca finals 2 months ago! This forum is supposed to be where we air things out that shouldn't be thrown around as gospel rite? Hmmmmmmmmm.....


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## thehatedguy (May 4, 2007)

One of the finest cars that I've heard in a long time ran analog out of his Denon deck to two daisy chained DSP6s.

His signal went D/A, A/D-D/A, A/D-D/A, and finally to the amps.

Each output of the first DSP-6 was run into a seperate input of the 2nd DSP-6 to get more EQ flexibility.


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## ncv6coupe (Oct 25, 2009)

20 PEQ bands per channel WOWSERS. Did said guy do RTA? He must be kicking mucho A$$ if he competes. Another thing I've been noticing is the momentum towards measurement tuners on here. Seeing something on the screen can blur your senses on what you are hearing when you start turning knobs and analyzing them changes too much. Are car audio guys pushing theirselves to "audiophile" status inadvertently? Seems so to me, maybe I'm full of it though.

To make it clear though, I definately have no issues with using as many tuning tools you have at your disposal, having the Edge should never hurt right Now what to do with these 31 band EQ's and get my parametric game going. I'm tempted to get a dsp 6 but then i have to invest almost another grand for the entire setup, that's the tough pill to swallow for only a flatter frequency response.


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## ungo4 (Jun 5, 2009)

I do believe that multiple conversions degrades the dynamics of a system some. It is a very small change and one that I could probably not tell outside of my own system that I am intimately familiar with. There are a multitude of other things in a system that will affect a system more than this so in the overall scheme of things it will probably make no difference what so ever to all but the most golden ears. And to be honest it may be a thing more in my head than a real difference that I hear so there.


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## thehatedguy (May 4, 2007)

It was in "the other hated guy"'s white Accord before it was totaled. It took 2nd in the top 30 round at ESN the only time it competed...and it wasn't really tuned- Randy and Matt Roberts just started tuning it that weekend. What they did was use one set of EQs to get a flat FR and the other set of EQs was in the tuning for taste. And they did some crossover shaping that way too by pulling down the EQ around the XO points you could create specific roll offs.




ncv6coupe said:


> 20 PEQ bands per channel WOWSERS. Did said guy do RTA? He must be kicking mucho A$$ if he competes. Another thing I've been noticing is the momentum towards measurement tuners on here. Seeing something on the screen can blur your senses on what you are hearing when you start turning knobs and analyzing them changes too much. Are car audio guys pushing theirselves to "audiophile" status inadvertently? Seems so to me, maybe I'm full of it though.
> 
> To make it clear though, I definately have no issues with using as many tuning tools you have at your disposal, having the Edge should never hurt right Now what to do with these 31 band EQ's and get my parametric game going. I'm tempted to get a dsp 6 but then i have to invest almost another grand for the entire setup, that's the tough pill to swallow for only a flatter frequency response.


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## Sarthos (Oct 29, 2010)

I'm afraid the question here is a bit vague...depending on the circumstances it may or may not make a difference. Here's a few situations.

1. Noise
If your RCA wires are picking up noise on their way to your processor, digital cables will help reduce the noise. If they're picking up noise between the receiver and amplifier digital cables will not help (unless you have digital cables to the amplifier). If you are getting noise from a component, digital cables *probably* won't help. It is possible noise is coming from an analog component in your headunit, in which case digital cables would help but most likely that's not the case

2. Number of components. I can't remember the name of the process, but in the case of digital images, there is a method of finding out whether they have been doctored by re-saving them over and over again or compressing them and decompressing them, something like that. Each cycle changes the image by a tiny amount, almost impossible to notice. However, this is done many times and the result is that after enough cycles, the image looks very different from the source image and anything doctored will stand out a lot. If you have a LOT of separate processors, digital may help, if not it probably not

3. Quality of components
Running a Bitone off of an Eclipse sound monitor? You shouldn't be able to tell the difference between RCAs and optical. If you were running a cheap Sony Xplod, you'd probably notice a significant difference between RCA and optical. In fact, you'd notice the Xplod would sound a lot more like the sound monitor if you left all the EQ features alone. The catch: Cheap headunits don't have optical outputs. The actual digital signal that different units get from the laser reading the CD is almost identical even for very different headunits. By getting that signal directly, a cheap headunit can sound like a very expensive one

4. What are you bypassing with digital cables?
Bypassing a 1-bit digital/analog converter? (Or multiple 1-bit converters?) might be noticeable. Not very, but if you listen really close...
Bypassing an entire unit of your system? Like if you have a CD changer/HD receiver/DVD player/etc -> headunit -> processor, and you use a digital output to bypass the headunit altogether, it should be noticeable.
Bypassing an undesirable stage of processing? If you have a stereo which is built for iPod playback, it may have built in bass restoration processing that makes iPods sound better, but CDs sound worse. Skipping that processing will indeed be noticeable.

4. OEM integration
Love your stock stereo but want great sound? Using the high level speaker outputs vs modifying the stereo to have optical outputs is no contest.

5. Headunit heat issues
This one gets really complicated. Basically, I'm sure everyone here knows that if you have a headunit with an internal amplifier, the headunit can heat up and skip while playing CDs, especially in the summer. If you turn the internal amplifier off (or run a good headunit like an Eclipse which doesn't have one) you will generate even less heat and you shouldn't skip. If you run a digital output you can take it to the next level by not generating heat from the pre-amplifier, cooling your headunit even more. This could mean no risk of skipping CDs from heat, or if you're really lucky it could raise sound quality if the CD heating up was making for bad sound, or if the heat from the pre-amplifier was causing clipping.

Those are the main things I can think of...


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## tornaido_3927 (Nov 23, 2009)

Genxx said:


> Long ago there is a thread about cables that people have used that are as cheap as buying RCAs that work with the Zapco amps.


I found that the din cables used for mice and keyboards of old (before USB became the rage) work perfectly with the Zapco units, and they're only a few dollars each


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## St. Dark (Mar 19, 2008)

Sarthos put it well.
It CAN make a difference, depends on the situation and the quality of parts you are bypassing.
Other times you might be hard pressed to tell the difference with the best of gear in a dead silent room.

Since the answer isn't empirical, you could say it's a Myth that Digital to Digital ALWAYS sounds better...but be aware that doesn't mean it might.

As mentioned, stock integration is a great candidate- tuned an Audi with a Bit One, then later added the Mobridge digital adapter once they came out...it definitely helped.


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## t3sn4f2 (Jan 3, 2007)

The OP asked if I could share some measurement results I posted elsewhere which have to do with this topic. These are analog and digital input/output measurements of my soundcard ($100 EMU 0404PCI soundcard, $10 Hosa RCA's).

The following results are what is called a "loopback" test where you take the output from the soundcard and plug it into the input of the same card. So in essence it is the same thing as going from an A to D>D to A of a processor but only inverted where it is a D to A>A to D. The measurement software (Rightmark Audio Analyzer) works by creating a test file of the resolution format you choose, which you then play from the component that you want to test. 

The results are a combination of the output quality of the component being tested PLUS the input quality of the measuring device. As are all component test you've ever seen. As long as the measuring device is much cleaner then the device being tested then the measuring device won't taint the result with it's own character. 

The software records and analyzes the test file recording and displays it as your typical dB and % numbers along with a graphical representation. I recorded in 24bits for all test in order to keep the ADC from contaminating the 16bit format's results.

The chart below is are four separate test runs on the same hardware configuration. The only differences are the resolution and whether a Toslink digital loopback test was done or an analog test. 

Results Summary:









Frequency Response:









Noise Floor:









Dynamic Range:









Total Harmonic Distortion, THD (for 1Khz at -1dB):









Intermodulation Distortion, IMD:









Stereo Crosstalk (ie Stereo Separation):









IMD Sweep:










The first column results are of an analog loopback test BUT the playback resolution is only at the CD formats limit (ie 16bit/44.1kHz). This corresponds only to what the analog out measurement of a CD format would be.

The second column is the digital loopback result for a CD format (ie 16bit/44.1kHz). These are perfect results, identical to the test files own results. Bit perfect IOW and the best a CD can do.

The third column is the one that counts. As you know, modern processors have 24bit ADC's and DAC's. This is an ANALOG loopback test but using a 24bit/44.1kHz high resolution test track in order to remove from the results the resolution limits of a CD format (ie 16bit/44.1kHz). IOW, a 24bit digital resolution is sooo much better then what any modern ADC/DAC can do (as can be seen in the last column), that when it is run through them the results are exclusively the analog circuit's performance. Unlike when a CD format's resolution is run through them. As you can see from the other results.

Results discussion:

Notice that except for .0011%'s worth of THD the 24bit analog loopback is in every way better then a perfect CD digital output can achieve. Even in the more important IMD.

It terms of noise added, the 24bit analog loopback blows away what a CD can do. The results show that IF the source and the processor are of very good quality AND they are installed properly, then there will be no lose of quality from the extra D to A A to D since a CD's digital resolution potential has been surpassed by modern ADC/DAC's analog performance. _To the point where they don't change the signal to any meaningful measurable degree. _


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## t3sn4f2 (Jan 3, 2007)

And I did not send anything to the dumb questions forum damn it!


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## ErinH (Feb 14, 2007)

but, what sources are 24/96 capable? Very few that I know of (alpine f1 dvi 9990 and clarion drz9255, for example) are capable of this resolution.
looking at the summary chart it seems obvious the benefits are dynamic range and lower noise floor.
So, how do we actually achieve this?


I do like the mentioning of the extra d/a conversions. good test data there, Frank. 


I notice that the following charts show some odd behavior and may just be a copy/paste error:

_Dynamic Range _and _Total Harmonic Distortion, THD (for 1Khz at -1dB) _look the same. Double plot post?
The _Stereo Separation _charts are lacking L/R data; rather they just have a single line for each test. Was this intended or just a mistake in plot posting?

Discussion:

What's with the large spike @ 1.2khz on the 24 bit digital test? 
Also, with the IMD data for all samples, there appears to be 60hz 'noise' here. Was this on a laptop that was plugged in? I've had issues with 60hz getting into the system and creating a buzz. Odd that I'm not seeing harmonics of this on the 24bit digital sample, though, so it makes me question if this is indeed an AC power issue. 
Interesting the the IMD % decreases on the 24bit sample, whereas it pretty much stays constant with the other samples.


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## t3sn4f2 (Jan 3, 2007)

bikinpunk said:


> but, what sources are 24/96 capable? Very few that I know of (alpine f1 dvi 9990 and clarion drz9255, for example) are capable of this resolution.
> looking at the summary chart it seems obvious the benefits are dynamic range and lower noise floor.
> So, how do we actually achieve this?


These were all taken at the standard CD sample rate of 44.1kHz. If I were to bump it up to 96kHz there would be little or no difference in the numbers. Except that the frequency response would extend past 30kHz on the 96kHz 16 or 24bit results (even the analog one). The bit rate affects the dB scale and the sample rate affects the bandwidth of the test.

It's also hard to tell the results apart in these test since when they are identical and the graph can only show one color, but you can zoom in a pic them out in small discrepancies. The blue and white fall off together since that is the analog signature of the card along with the digital format's limit. The purple and green extend out past 20kHz. My FR pic doesn't show it but the digital FR results tapper off at the corresponding sample rate limit which is just off the screen for 16bit/44.1kHz.



bikinpunk said:


> I do like the mentioning of the extra d/a conversions. good test data there, Frank.


Thanks, and thanks for the questions. I'm a little scatter brain with these presentations so I don't always fill in all the blanks as I should.



bikinpunk said:


> I notice that the following charts show some odd behavior and may just be a copy/paste error:
> 
> _Dynamic Range _and _Total Harmonic Distortion, THD (for 1Khz at -1dB) _look the same. Double plot post?





They're actually different. The DR test tone is at -60dB whereas the THD is -1dB. Showing the dynamic range potential by play an extremely low level signal and looking for what happens to the adjacent frequencies.



bikinpunk said:


> [*]The _Stereo Separation _charts are lacking L/R data; rather they just have a single line for each test. Was this intended or just a mistake in plot posting?



That's a software limitation. Whenever you do a comparison plot of more then one test it averages together the left and right of each result in order to keep the craziness on the screen down. They also aren't that much different from each other, only a few dB between left and right.



bikinpunk said:


> Discussion:
> 
> What's with the large spike @ 1.2khz on the 24 bit digital test?





I'm not 100% sure but it has to be how the RMAA software's 24bit test tone look like at that extremely low level area since it is identical to the way the reference 24bit test file looks like when I analyze it directly without playback or recording it. 



bikinpunk said:


> [*]Also, with the IMD data for all samples, there appears to be 60hz 'noise' here. Was this on a laptop that was plugged in? I've had issues with 60hz getting into the system and creating a buzz. Odd that I'm not seeing harmonics of this on the 24bit digital sample, though, so it makes me question if this is indeed an AC power issue.


That one I have no clue about, it can't be 60Hz hum because it is not on the other blue plot which are measured seconds apart during the test. They are also not there in the 16bit analog test which is even stranger, since their lack on the other plots would indicate some type of signal dependent harmonic, yet it's not on the 16bit analog plot. 



bikinpunk said:


> [*]Interesting the the IMD % decreases on the 24bit sample, whereas it pretty much stays constant with the other samples.



Yup, that a great thing though since IMD is a more complex signal that would relate more to music and how the ADC/DAC handles it. Since they are lower in level and more along the lines of the average amplitude of music. Shows that the extra conversion is even less significant were it matter most in the music.


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## ErinH (Feb 14, 2007)

Cool! Thanks for the answers. One day, you'll have to dumb this program down for me so I can use it myself.


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## ncv6coupe (Oct 25, 2009)

^^Thanks guys, I was waiting for t3sn4f2 to post the graphs before I commented on the above. Do any of you guys have any rta or rather amplitude measurements of tweeter hiss? 

It would be great to get a pic of the frequencies affected by the noise relative to what we would percieve as dynamic range in the highs of music.

Reason I ask is; I have some tweeters that show extension to 30khz. I can hear some super highs if the tweeter is close enough against my ear and this is with a regular panasonic home audio receiver. I haven't put them in the car to test yet. I was reading the clarion drz manual and they sort of went on a rant (claiming superiority *subliminally of course*) about dynamic capability of the receiver BECAUSE it has the 24bit 96khz DAC's. Now I'm not going to be the one to question clarion's marketing or research but I felt like it was quite the crock of ____! Phase shift at 40khz









Any pics of tweeter hiss anyone?? More discussion to follow.


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## t3sn4f2 (Jan 3, 2007)

ncv6coupe said:


> ^^Thanks guys, I was waiting for t3sn4f2 to post the graphs before I commented on the above. Do any of you guys have any rta or rather amplitude measurements of tweeter hiss?
> 
> It would be great to get a pic of the frequencies affected by the noise relative to what we would percieve as dynamic range in the highs of music..


Not clear on the type of hiss you mean. There's hiss from the CD resolution's limit (ie -97.8dB relative to nothing. Dead silence could be being recorded in the quietest room, with the best mic and the best ADC and you would still not get quieter then that since the noise is native to the format limit). Then there's the added analog circuit noise from the ADC and/or DAC that the digital file is converted through (insignificant if the converters are quality and the bitrate is high enough). And finally the background noise from the environment itself, which is IME MUCH louder then the other two.



ncv6coupe said:


> Reason I ask is; I have some tweeters that show extension to 30khz. I can hear some super highs if the tweeter is close enough against my ear and this is with a regular panasonic home audio receiver. I haven't put them in the car to test yet. I was reading the clarion drz manual and they sort of went on a rant (claiming superiority *subliminally of course*) about dynamic capability of the receiver BECAUSE it has the 24bit 96khz DAC's. Now I'm not going to be the one to question clarion's marketing or research but I felt like it was quite the crock of ____!
> 
> Any pics of tweeter hiss anyone?? More discussion to follow.


The DRZ up samples the 16bit/44.1kHz CD files from the transport or digital input by way of an asynchronous sample rate converter (ASRC). That produces a virtual 24bit/96kHz representation of the original format that from how I understand it, is more accurately processed in the DSP. Once processed, the DAC converts that most probable 32bit stream (of 96kHz) with its more then likely 24bit/196kHz DACs. Almost all ADC and DAC chips are capable of that now, they just don't run that high depending on the digital stream coming in and they don't perform anywhere near that digital resolution's potential. 

I can't comment on how that affect dynamic range though.


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## ncv6coupe (Oct 25, 2009)

Tweeter hiss or maybe more commonly known as gain hiss. You know the skkkkkkkkkkkkkkkkk static. 

I downloaded a 1 minute digital silence track to check my hiss(es) and noise levels. 

I also only tune at night, late night in an under house garage with the lights off. Not much environmental noise down there at those hours.

I also like the sound of cheap kenwood excelon radio's.


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## ErinH (Feb 14, 2007)

noise isn't at a specific frequency. typically the noise we hear is due simply to the SNR levels and spans a pretty large passband. noise gates, iirc, essentially look at the input noise and then takes the differential of the signal vs the noise. Chad, or someone else, would have to chime in on this, though.
I'm horrible at explaining it, but I think this site should cover you:
Noise Removal - Audacity Wiki

IOW, it's not as simple as adjusting a couple bands. You'll diminish the noise, but at what cost? Lost dynamics, lost ambiance, lost snap??? There's always a trade off. Whether or not the trade off is acceptable depends on the car, install, and listener.

The best thing you can do is to simply focus your attention on your gains. In most every case, the issue with noise floor - especially on tweeters - is because the amp(s)' gain on the tweeter is cranked up.. whether on purpose or by default (ie: you have the mid and tweeter of one side shared on an amp gain). In most of these cases I've noticed that the tweeter is either attenuated quite a bit (more than a few dBs) or there are severe cuts in the passband. What this tells me is that the tweeter is too hot and the user is cutting bands to tame the hotness, where all was needed was a lower pot placement at the gain. Then you've lowered the noise floor and solved your problems. In short, the user gets caught up in cranking the gains because in their mind higher gain = better sound quality... while in most cases, especially tweeter, this is the total opposite. 

On the flip side, you may also find that you get more 'hiss' when you boost the 10k-20khz range to make up for an off-axis tweeter install... increasing the signal going to the amp and increasing the noise floor of that passband, relative to the rest of the tweeter's passband.... making it more audible. Make sense? 

So... what I'm saying is this: *check your amp gains if you have hiss*. In nearly every case I've had or helped with, hiss is tied to SNR and the amp gain pot is the root of the problem. You don't really need 150w going to your tweeters. 


Edit: Hope that makes sense and helps.


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## ncv6coupe (Oct 25, 2009)

Oh yes bikinpunk, makes lots of sense! Great points on the tuning out hiss, losing lots of necessities in the goal of ultimate sound. 

That's why I asked for a (microphone'd rta'd) version of it. I can pick this up in certain critical listening but I too am not the best at explaining myself online. 

Audacity link=greatness

PS.
I'm a lazy a$$. I run JL amps like everyone else too


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## ErinH (Feb 14, 2007)

I've rta'd hiss before, which is why I said it's hard to peg it down to a specific frequency. It's broadband... just like the pink noise you use to test it with, except it's white noise instead. 
http://www.sweetwater.com/expert-center/techtips/d--08/23/2000


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## ncv6coupe (Oct 25, 2009)

ungo4 said:


> I do believe that multiple conversions degrades the dynamics of a system some. It is a very small change and one that I could probably not tell outside of my own system that I am intimately familiar with. There are a multitude of other things in a system that will affect a system more than this so in the overall scheme of things it will probably make no difference what so ever to all but the most golden ears. And to be honest it may be a thing more in my head than a real difference that I hear so there.


Ungo, Take a look at the graphs that were posted earlier. Pretty shocking results, No subjectivity there. I can agree with you considering your background and knowing exactly what you are listening for. I can hear really high frequency but the degradation part I'm not so sure about. Thats why I put it out there for everyone to chime in on in a sensible way. Its when people get forceful about their beliefs when you have to call BS on them.


Sarthos, Thanks for that great breakdown of the various troubles that everyone will run across when putting together any amplified car audio system even the OEM factory. I notice you mentioned that the digital image looks different through the various sampling steps which t3sn4fn broke down the process excellently. If you didn't know this, it might still sound the same though..... The day of the OEM dead head is right around the corner, automobile specific DSP in the underseat built in amplifier will be standard and 61.1 surround sound will be the "Bose" upgrade .

Bikinpunk, Do you think you still have those pics? I knew a tweaker like yourself has done all this. I would do it too if I would just get a good USB preamp but I'm afraid of what I'll create when I do. I figure it has to be such an annoying sound because you'd have to crank your stereo up pretty loud with nothing playing to get a good reading of it. If you can find it, could you post it? Thanks


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## t3sn4f2 (Jan 3, 2007)

ncv6coupe said:


> Oh yes bikinpunk, makes lots of sense! Great points on the tuning out hiss, losing lots of necessities in the goal of ultimate sound.
> 
> That's why I asked for a (microphone'd rta'd) version of it. I can pick this up in certain critical listening but I too am not the best at explaining myself online.
> 
> ...


You can see what hiss looks like on the noise floor graph. That is a specific portion of the test track that plays with no tone or other obvious test signal, only the hiss that the resolution will produce. The digital result is the purely the hiss that comes with that format resolution. No analog hiss is added.

That hiss level, even at only 16bit tends to be very low compared to component hiss down the line. Like the tweeter over gain hiss Bikin mentioned. And even worse then any of those is the recording hiss from even the best recording. 

They all add up though, but they have to be fairly close in amplitude to actually audible add up to something louder. For instance, if I play a -97dB white noise track and then play another of the same track along side at -97dB also, the resulting amplitude will not change any. I have to bump up on of the track to almost -15dB in order for the overall output to increase 1 signal dB. That is why s/n ratios are only ever evaluated on there own. there is never a concerned of if they will add up to something audible once all the component are in-line. They are soooo low in level that they can not add up to something audible unless one is broken. Only when one component is overdriven to an extreme point where it's own noise floor is unnaturally amplified will the noise become a problem. That is what gain structure is all about. Playing with the volume of each device till you get the lowest overall noise from the right combination of settings. 

One of the best ways to combat hiss is to control the master volume from the last component in the signal chain (ie JL HD amps with their addon HD-RLC MVC knob). What that does is attenuate any his from the signal chain along with the signal. It keeps the signal to noise ratio constant, and if it not good enough, it bring the noise down in amplitude to a level that is inaudible. 

The opposite is true for master volume control from the first component. Any noise from the output stage that is there after the volume control won't be attenuated, it's seen as constant regardless of volume setting. Any noise picked up on the transmission chain won't be attenuated, it's constant. any noise added by another device won't be attenuated. All because you are only attenuating the signal at first and not the noises afterward.

This is kinda an optimum way of looking at it and probably not a problem for all but the most dynamic systems. If not people would not be doing MSC from the head unit.

It's also not a big deal during music playback since the hiss from a recording will be much louder then the hiss from the system. It's only an issue for someone that doesn't want any noise from their system when it's just sitting there with no music playing and the volume knob at max. And most head unit mute the outputs when no music is playing anyways ("zero bit mute") so it takes the head unit out of the noise contributers. That's a clever way head unit manufacturers make the head units appear to have excellent S/N ratios, instead of the component hiss being so low that it can not be heard while no music is playing you simple mute the output and unmute it during playback which then the component noise is no where near as loud as the recording and and does not add to it hardly or noticeable since there is no way to compare and know that the added noise is not part of the song. Pretty smart.


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## St. Dark (Mar 19, 2008)

ncv6coupe said:


> ^^Thanks guys, I was waiting for t3sn4f2 to post the graphs before I commented on the above. Do any of you guys have any rta or rather amplitude measurements of tweeter hiss?
> 
> It would be great to get a pic of the frequencies affected by the noise relative to what we would percieve as dynamic range in the highs of music.
> 
> ...


Keep in mind that just about any digital material you have will be frequency limited to 22k (typical 44.1kHz sampling rate).

And yes, the 24bit DAC does have a better potential dynamic range...but of course it won't do any better in reality than the material you play through it (which will typically be 16bit). One reason - << pure conjecture on my part >> - that they may have used that DAC was to upsample as mentioned by t3 so as to be able to run the onboard digital processing on a higher bit rate/sample rate stream, and to have "headroom" in the digital signal to accommodate say EQ boosts when the material approaches 0dB at that frequency.
Plus of course the marketing department can now claim 24Bit!! 96kHz!! (and we know marketing has so little to do with car audio gear...*L*)


Also, to a degree OEM deadheads are around and have been for a bit. A lot of the mid/upper end systems send a line level back to the stock amp; some (GM Bose and Infiniti in some cases) even send a stereo fixed level back, and the dash unit sends volume/fade/etc commands to the amp through the databus. Plus of course the MOST systems that are all digital from piece to piece and converted inside the amp. And there are integration companies working on amps such as you speak of- where you'd replace the stock amp with one that still feeds off of the MOST digital fiber loop but has more power and lets you get to the EQ and such (versus the stock ones which are often heavily EQ'd...you just can't get in and change anything). I hope you're wrong about the 61.1ch Bose systems *L* but you're pretty dead on with the rest of it.


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## Sarthos (Oct 29, 2010)

I like the graphs, the digital to analog conversions vs digital output are so much better than the resolution of a standard CD it shouldn't make much of a difference. And if you're using a tuner or if you really don't care about SQ at all and are using an iPod ( :'( ) it shouldn't make any real difference. 

I don't know if you have the equipment to pull off this test though. Same tests, only instead of 16 bit/44 kHz sampling for the CD, do some tests for higher quality source units. 16 bit/48 kHz for DVD quality, or dun dun dun...
16 bit with 96 or 192 kHz sample rate for Studio quality
24 bit with 44, 48, 96, or 192 kHz sample rate for uber studio quality.


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## t3sn4f2 (Jan 3, 2007)

Sarthos said:


> I like the graphs, the digital to analog conversions vs digital output are so much better than the resolution of a standard CD it shouldn't make much of a difference. And if you're using a tuner or if you really don't care about SQ at all and are using an iPod ( :'( ) it shouldn't make any real difference.
> 
> I don't know if you have the equipment to pull off this test though. Same tests, only instead of 16 bit/44 kHz sampling for the CD, do some tests for higher quality source units. 16 bit/48 kHz for DVD quality, or dun dun dun...
> 16 bit with 96 or 192 kHz sample rate for Studio quality
> 24 bit with 44, 48, 96, or 192 kHz sample rate for uber studio quality.


It can, I'll try to run them this week. I ran into another test online and it appears that higher sample rate helps out the noise floor a little as well, although I'll have to verify it with my card. I though it just increase bandwidth, but it seems to reduce the noise floor by 2 or 3dB. Insignificant I know but worth noting.


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## Silver Supra (Feb 15, 2008)

On a somewhat related note, I wish the Bit one had DAC's/output stage which could come close to my NAK CD700II. After all the hassle of installing the Audison and feeding it a raw digital output (coax) I ended up going back to the analog output of the NAK because it just sounded better. 

I'm pissed because the flexibility of the Bit One is fantastic, but in the end it just wasn't as good as my HU.

Anyone else experience this?


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## thehatedguy (May 4, 2007)

I dunno...I will tend to side with the man who was on the design team of the first multibit DAC and made a very successful career of designing ADCs and DACs and say that conversions today are so good that you will not hear a difference in the conversions.

What happens before/after the conversions would cause more of a sonic problem than the conversion itself. I would suspect that is where the problems would come from.


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## thehatedguy (May 4, 2007)

Well that person who I am referring to has over 100 patents in the analog side of things. 

I would say he knows audio engineering.


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## St. Dark (Mar 19, 2008)

Silver Supra said:


> On a somewhat related note, I wish the Bit one had DAC's/output stage which could come close to my NAK CD700II. After all the hassle of installing the Audison and feeding it a raw digital output (coax) I ended up going back to the analog output of the NAK because it just sounded better.
> 
> I'm pissed because the flexibility of the Bit One is fantastic, but in the end it just wasn't as good as my HU.
> 
> Anyone else experience this?


*L* Yeah, but look at the price of the Nak...and it only had 2ch worth of DAC.

If they ever do a Thesis version like they initially threatened, you'd probably get your cake and be able to eat it, too. Although, since the B1 sends a digital feed to the Thesis amps (and the LRx replacements, soon) I have to wonder if it will ever happen.


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## Silver Supra (Feb 15, 2008)

St. Dark said:


> *L* Yeah, but look at the price of the Nak...and it only had 2ch worth of DAC.
> 
> If they ever do a Thesis version like they initially threatened, you'd probably get your cake and be able to eat it, too. Although, since the B1 sends a digital feed to the Thesis amps (and the LRx replacements, soon) I have to wonder if it will ever happen.


Yeah I agree. I have been told the DAC's in the Thesis amps are higher quality than the B1, but I don't have the $ to find out. 

I've heard rumors of a Thesis version B1 too and think it would be great... but then they'd probably sell less Thesis amps. Probably not their business model. haha


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## 14642 (May 19, 2008)

So...do this experiment. 

1. View the waveform of a piece of music as a .wav file.
2. Compare that to the waveform after compressing it to MP3 at 320k
3. Compare that to the waveform at the output of every subsequent piece of electronic equipment in your system, but make sure it goes through a bunch of ADC/DAC/ADC/DAC conversions.
4. Compare that to the waveform recorded using a microphone placed in the listening position. 

Hmmm...I'd say the best bet is to focus on the acoustics.


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## St. Dark (Mar 19, 2008)

So, summing up, we have it that Direct Digital Transfer in and of itself being Clearly and ALWAYS better than converting to Analog and then back into Digital, is a *Myth*. Jeff Scott (the person hatedguy alludes to) has said this for some time now; and we have posts in this thread supporting it.

That being said, careful reading of the thread will reveal that the converse- that the two options are ALWAYS identical, is also not valid. The (analog) circuitry in between and specific situation at hand CAN lead to digital direct being better (interfacing to an OEM system, for instance). You also can have benefits with minimizing the places noise can get in, or by moving the master volume control "farther downstream", but the D/A conversions or lack thereof specifically addressed in the OP are not going to have any real affect with current equipment of decent quality.
Know what your end goal is, and juggle the trade-offs you'll encounter in each specific case getting to that goal accordingly.


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## ErinH (Feb 14, 2007)

Andy Wehmeyer said:


> I'd say the best bet is to focus on the acoustics.


dun, dun, duuuuuuunnnnnnn


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## t3sn4f2 (Jan 3, 2007)

"TRANSPARENCY: If op amps really have a “sound”, as many audiophiles suggest, it would follow when you add op amps to the signal path the sound should change. *Two guys named Meyer and Moran  (<~link) conducted a very interesting rigorous study. They played high resolution SACDs on a high end system and sometimes inserted an extra A/D and and D/A into the signal path to “down convert” the high resolution audio to CD quality (16/44) audio. After 500+ trials lasting more than a year, using audiophiles, recording engineers, and students as listeners, they found nobody could tell when the extra A/D and D/A was in the signal path.* On top of demonstrating the supposed benefits of SACD are highly questionable they also managed to demonstrate that A/D and D/A converters can be audibly transparent as well. And, as you may have guessed, both the A/D and D/A add several op amps to the signal path. But nobody could tell they were even there. There have been many more blind tests that also demonstrate different op amps (and much more) indeed sound so much alike even audiophiles can’t hear the difference. See the Matrix audio test  (<~link) for another example."

This quote covers three things really.

-High resolution music sound better than CD.
-An ADC/DAC conversion instead of a straight digital interface will audibly degrade the signal.
-Op-amp have a particular sound to them.

Hell you can even throw the cable myth in there since the extra devices need to be interconnected somehow. So how can a cable sound better than another if it can't make something sound different. (Please don't say because the system as a whole sound so bad that the high end cable fidelity is hidden behind the garbage. )


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## ncv6coupe (Oct 25, 2009)

Frank, I must applaud you for your consistent sourcing of pure objective research that introduces truth to the audio nuts on the forum. Thanks for the new and even more refreshing links.


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## MarkZ (Dec 5, 2005)

t3sn4f2 said:


> "TRANSPARENCY: If op amps really have a “sound”, as many audiophiles suggest, it would follow when you add op amps to the signal path the sound should change.


I think audiophiles just like to spend money. Because very few of them ever say they prefer NO op amps over their boutique op amps. Most of the time, you can rip your buffers out of your amps and the D/As in your sources are usually stable enough to directly drive the load without its intervening op amp too. I don't usually see _these_ types of mods in audiophile circles.


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## t3sn4f2 (Jan 3, 2007)

ncv6coupe said:


> Frank, I must applaud you for your consistent sourcing of pure objective research that introduces truth to the audio nuts on the forum. Thanks for the new and even more refreshing links.


Thanks man


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## feeshta (Oct 2, 2011)

The perfect system would be the original analog signal directly feeding a very simple amplifier with as few components as possible (open ended design), which feeds 2 theoretical full range speakers placed an equal distance in front of the listener. The problems with this system in an automotive environment (or any environment for that matter) are obviously myriad, but the closer you can stay to that model, the better. 

The first issue is with the reproduction of analog sources. They are inherantly vulnerable to degradation. No two capacitors or resistors are EXACTLY alike, so they inherantly are going to change the signal in some small way. To solve that issue, digital technology offers an easy way to ensure quality reproductions of the original recording which are always identical. Even thought they not quite as good as the original, they can be easily reproduced exactly, with no loss. 

In my experience, keeping things in the digital realm as long as possible decreases the chances of signal degradation because as long as you can still tell the difference between a 1 and a 0 with 100% accuracy, there is no signal degradation. Using high quality converters and components does make it possible to achieve conversions that are not audible, so if you must do it, all is not lost. But, the best policy is to try to stay as close to the ideal as possible. So, all things being equal, you should choose the method that involves the least convertions etc. 

In the car audio environment, there are myriad factors that change the sound, and having tools to combat and correct these changes can be more beneficial to the overall sound than the small amount of change introduced by an extra D/A or A/D conversion by far. Ideally though, you would have a system that allows you to make all of these tweaks in the digital realm, and have the best of both worlds. 

It's all about compromises, and finding the path that affords the fewest of them.


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