# Understanding DSP Output Voltage in Relation to amp input sensitivity



## Jamesj562 (May 26, 2020)

My Helix P-DSP can take 3v input and outputs 4V. My factory low level pre amp signal rcas feed directly into the DSP, however for output from the DSP should I base all gain settings off of the advertised 4V output of the DSP?

For example my JL 1000/1 takes low level signal from 200mmV-2V or High Level Signal from 800mV-8V. Would I select the high level signal for rcas going from my dsp into the JL 1000/1?

Also my 10ZX650.4 Kicker 4 channel Dows low level inputs of 125mV-5V and High level 250mV-10V. Am I correct in setting this to low level based on the dsp output of 4V. 

The part that is kinda throwing my off is the concept that id feed low level preamp signals into the DSP yet the would come out higher than what went in and on the JL slash amp be higher than the low level signal ratings.

Thanks for helping a newbie!!!


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## Blue_Horseshoe (May 14, 2020)

You want low level selected for your amp inputs. You are using an in-amplified signal.

High level would be if you were connecting the speaker wires, with an already amplified signal from your head unit, to your amp.


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## Muu (Jan 22, 2020)

Right so this comes down to a question of gain structure, ie using as much of the headroom as a you can to not leave power / resolution on the table but also not pushing the amp or ADC into clipping. If you want to do it right you'll need either a oscilloscope or a gadget like the one from SMD that gives you a light when distortion (ie clipping) kicks in. Route I'd take is:


Create a 0dbFS reference file (or maybe just under) of say a 1k tone
Play the tone on your HU and look at the waveform on the scope, raise the volume until you see the peaks clip and then back it off. That is your max gain with your source unit, take a note what volume the HU clips out at.
Run the outputs into the DSP and set the input gain as high as you can go before it clips, this way you're using as much resolution as the DSP ADC has. For example that might be about 2.3V peak to peak, so you'll want to map that peak to peak of the 16bit ADC (or whatever it is).
In theory then your input gain will now map to 4V from the DSP DAC output and should be clean - I'd check it though.
Bring the DSP output into the various amps, and put a dummy load on the terminals with your scope in parallel. Set the input gain on the amps until they clip, then back it off.
That should leave you with a perfect gain structure, but requires time and patience and should leave you with a clip free syetem. Some will advocate running the gain structure harder, an extra 3db is of course a doubling in wattage and they'll fairly cite that much tracks often have a overhead built into them - I don't disagree entirely but really it's good to have a known clean gain structure especially when you're going through multiple stages of AD/DA.


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## JaySea20 (Jun 21, 2020)

Blue_Horseshoe said:


> You want low level selected for your amp inputs. You are using an in-amplified signal.
> 
> High level would be if you were connecting the speaker wires, with an already amplified signal from your head unit, to your amp.


Correction: The JL Slash series uses that switch for "high" low level inputs. Meaning that if you have a HU or, most likely, a Line Driver Putting out 6-8v signals, you flip that switch to high. It has nothing to do with speaker level inputs.

I have run Slash series for years. If you have anything above 4v going into your amp, you are playing with fire leaving that switched to "low"... At the normal 3-4v I generally keep it switched to "high" just to make sure im not working the amp too hard.

-Jay


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## Blue_Horseshoe (May 14, 2020)

My mistake. I stand corrected.


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## jtrosky (Jul 19, 2019)

My JL XD600/6v2 also has an "Input voltage" switch. Since my Helix DSP puts out signals up to 6v, I wasn't sure if I should leave the amp "Input voltage" switch on "Low" (200mv to 4v) or "High" (800mv to 8v). I emailed JL tech support and here is their response:


```
Hello, there is a bit of overlap for input voltage of the amplifier. Typically at 3/4 volume the average voltage out of a DSP is less than the full rated voltage. I would suggest having the input voltage in Low so that the least amount of gain can be used to achieve proper power output. This results in a higher signal to noise ratio. If you were in Low and were over the suggested target voltage with gain or sensitivity all the way down I would then switch to High. I hope this helps.
```
I don't know if the Slash amp "Input voltage" switch behaves like my XD600/6v2 or not, but just wanted to pass along the info.

I haven't had any issues whatsoever leaving the switch set to "Low".

And just to be clear, the switch on the XD600/6v2 isn't just for low-level or speaker-level inputs either. They even mention this is the manual when talking about the switch:


```
This is useful for certain high output preamp level signals as well as speaker level output from source units and small amplifiers.
```

EDIT: Just for "completeness", he is the exact question that I asked to get the response above:

```
I'm installing a PAC AmpPro4 and a Helix DSP.3 to go along with my XD600/6v2 amp. The AmpPro4 is connected to the Helix via a digital connection (optical). Since the Helix DSP is capable of 6V outputs, should I set the XD600/6v2 input voltage switch to High or Low? On the Low setting, gains end up around 10 o'clock. With the High setting, gains end up around 1 o'clock. However, the manual states that the "Low" setting is only for up to 2V input... I'm confused as to how I should be setting the input voltage switch. Please advise.

Thank you!
```


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## Jamesj562 (May 26, 2020)

That is the root of my confusion. It was easy prior to the DSP I ran low settings on both the JL AND the Kicker and it sounded very balanced and checked out on the DD1. 

Now with the DSP I run the JL on high and the Kicker on low but I’m considering bumping the kicker to high as well rather than try to align the 4V output to the very high end of the 5V max of the Kicker Low level input. Going to high setting for the amp input it will accept up 500mVa -10V


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## Destarah (Feb 24, 2019)

I was waiting to see how this progressed, I will throw my hat in the ring now. Run the amp at the Low setting. The only exception to this would be the following:
With the Low setting selected and the gains turned down fully down on the amp it is still clipping the input signal.

Bottom line is that keeping the gains low on the amp is generally a good thing. Switching to High and then needing to crank the gains up is not the best setup.


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## cman (Aug 24, 2020)

You want to be on the low setting. If anything just turn down the output of your DSP. This will keep the gain on your amplifiers as low as possible. I just switched my system over to a DSP with a higher output voltage and have since taken my amplifier gains from 3/4 to under 1/4. my dsp puts out 6v and one of my amps is only 5 volts max input sensitivity. Just like the JL tech said, you will know if its too much because your gain will be turned all the way down but youre still getting to a very loud volume at like 20% volume on your headunit. I just turn down those channels on my dsp output and im good. Your DSP only puts out the max voltage when its maxed out 100%


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## Jamesj562 (May 26, 2020)

UPDATE

Broke out the SMD DD-1 today after confirming my deck clip point I setup the kicker amp and on low input it was perfect maybe less than 1/4 turn and I was just shy of distortion on the DD1.

Now for the interesting part the JL 1000/1 on low input setting was clipping showing distortion at 0% gain with all EQs defeated. Flipped it to High Voltage inputs and less than 1/4 turn I was just a hair under the distortion point.


Cliff notes for a DSP with output of 3v the low setting on JL SLASH amps will clip at 0 gain. You must be in high input mode in order to properly set the gain. 
In hindsight this kind makes sense as the very maximum JL states is 2v input in the low setting.


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## crdi_lover (Jul 19, 2018)

Jamesj562 said:


> UPDATE
> 
> Broke out the SMD DD-1 today after confirming my deck clip point I setup the kicker amp and on low input it was perfect maybe less than 1/4 turn and I was just shy of distortion on the DD1.
> 
> Now for the interesting part the JL 1000/1 on low input setting was clipping showing distortion at 0% gain with all EQs defeated. Flipped it to High Voltage inputs and less than 1/4 turn I was just a hair under the distortion point.


What tracks are you using to set the gains on both the full range amplifier (Kicker) and subwoofer amplifier (JL Audio)?


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## Jamesj562 (May 26, 2020)

Track 4 on the SMD DISC for the kicker 4 channel 650.4
And track 3 for the Slash 1000/1 per the dd1 manual sq setup


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## sfarisminhas (Apr 4, 2019)

Muu said:


> Right so this comes down to a question of gain structure, ie using as much of the headroom as a you can to not leave power / resolution on the table but also not pushing the amp or ADC into clipping. If you want to do it right you'll need either a oscilloscope or a gadget like the one from SMD that gives you a light when distortion (ie clipping) kicks in. Route I'd take is:
> 
> 
> Create a 0dbFS reference file (or maybe just under) of say a 1k tone
> ...


So here is the thing:-

You stick your DD1 and scope on the end of a headunit and start turning the volume up to get the max unclipped volume. This is a 5v preout. At 40hz you clip at volume 48 and at 1k you clip at volume 46. You pick volume 46 as your safe volume. You then move down the chain to the TwK88 and you put the probes on the outputs of the TwK and start to measure. On volume 46 @ 1k you select 4v for the input sensitivity. This gives you a reading of around 3.6v and no distortion on the DD1. You set this on the rear channel too. You move onto the sub channel and play 40hz and pick 2.8v on the inputs, which gives you a reading of approximately 3.8v and no distortion. This seems to be the safest option that I have come across, there is something though, the meter on the TwK does show some red but the output does stay under the 4v limit. Now what do I do here? Do I increase the input sensitivity on the TwK so that there is no red that shows up, thus having to crank up the gain on the amplifier before the distortion light comes on and introduce a whole load of floor noise? Or do I keep the input sensitivity as it is as 4v and 2.8 respectively, which shows some red, no distortion on the DD1 and keeps the output at the DSP level under 4v and hence keeps the gain known slightly lower?


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## Muu (Jan 22, 2020)

Yeah I can't speak from experience on the DD1, I'd just use a oscilloscope and work down the chain.


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## sfarisminhas (Apr 4, 2019)

Muu said:


> Yeah I can't speak from experience on the DD1, I'd just use a oscilloscope and work down the chain.


Aren't you supposed to set up the DSP input sensitivity to match whatever the output is of your headunit? So if it's a 5v pre-out on the HU then on the DSP you would pick something this 5.6v, like for example on a TwK88? Picking a lower sensitivity ends up clipping both the inputs and the outputs of the DSP, but the DD1 tells me there is no distortion.


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## Muu (Jan 22, 2020)

sfarisminhas said:


> Aren't you supposed to set up the DSP input sensitivity to match whatever the output is of your headunit? So if it's a 5v pre-out on the HU then on the DSP you would pick something this 5.6v, like for example on a TwK88? Picking a lower sensitivity ends up clipping both the inputs and the outputs of the DSP, but the DD1 tells me there is no distortion.


So car audio seems to play by it's own rules, but effectively setting up gain structure is the same across all audio; you're trying to align the ranges without having a chain with say a high gain lifting the noise floor fed into a cut. I'd never trust what's printed on the box and much prefer to measure the signal and leave a sensible headroom. Maybe on the power stage you'll run it close as you can


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## Muu (Jan 22, 2020)

good article here: Gain Staging Like a Pro | Sweetwater.


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## sfarisminhas (Apr 4, 2019)

Muu said:


> So car audio seems to play by it's own rules, but effectively setting up gain structure is the same across all audio; you're trying to align the ranges without having a chain with say a high gain lifting the noise floor fed into a cut. I'd never trust what's printed on the box and much prefer to measure the signal and leave a sensible headroom. Maybe on the power stage you'll run it close as you can


The quandary started after I read this article, which steers away from what I have known to be standard convention.








Are scopes and sine waves useful when setting up DSP? - Audiofrog


scoping and 0dB sine waves aren't all that useful in a system that includes a DSP and some amps or some amps with DSP.




www.audiofrog.com


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## Muu (Jan 22, 2020)

Yeah that's a good article, ultimately the input stage of any digital device is about ensuring the ADC never reaches an output of: 1111111111111111 (if it's 16 bit). Once you clip a signal, you change its shape not just the amplitude, and no amount of gain reduction down the line will recover this deformation of the waveform.

What I feel Andy is talking about is when you start applying EQ / Gain / xover curves within a DSP that creates a net positive and if you're nearly out of digital words then you can still induce clipping, where the sine is squared off. Really you need some headroom in the input stage or ensure you're only subtracting in the DSP maths. You might sling a 1k 0dBFS tone into your chain and put a DD1 on the tail end and say "see, no distortion" but what if you had a EQ bump elsewhere in the frequency spectrum. Given decent DSP like the helix are 32bit DAC with 64 the bit processing you have 65k times the level resolution than your average music track, can more than afford to leave plenty of headroom in the DSP.

Obviously with the power amps we don't want to leave power on the table and people are keen to extract every last dB they can, sacrificing headroom for gain,


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## sfarisminhas (Apr 4, 2019)

Here is where it gets a little confusing for me. Before getting a dsp, it was straightforward. I would stick the DD1 probes into the speaker outputs of the amp and check both the max unclipped volume and 40hz and at 1khz. So let’s say my headunit clips at volume 47/50 at 1khz and volume 49/50 at 40hz. I would average it out and go for volume 46. Using that volume level I would set the gain on all the channels. Use -5db for the mids and highs and -10db on the sub. Turn the gain up until the distortion light comes on then back down until it goes out. Pretty straightforward right? Now, throw in a DSP. What I am finding is that the lower the input sensitivity I pick for example 1v the more the input clips. The higher it is for example something like 4v or 5.6v the less the input clips or there isn’t any clipping at all. But then you measure the voltage at the output section of the dsp the higher the number at the input side, the less voltage comes out of the dsp output, so when you move to the amp to set the final gain stage, you are having to turn the gain up more and thus inducing floor noise into the signal. Tell me if I’m doing something wrong here please? 😊


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## sfarisminhas (Apr 4, 2019)

The below are the settings of my DSP. The only thing that is left to do is to EQ. All the x-overs and delays are set. Am I doing something wrong, that is what I would like to clarify.


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## Muu (Jan 22, 2020)

sfarisminhas said:


> Here is where it gets a little confusing for me. Before getting a dsp, it was straightforward. I would stick the DD1 probes into the speaker outputs of the amp and check both the max unclipped volume and 40hz and at 1khz. So let’s say my headunit clips at volume 47/50 at 1khz and volume 49/50 at 40hz. I would average it out and go for volume 46. Using that volume level I would set the gain on all the channels. Use -5db for the mids and highs and -10db on the sub. Turn the gain up until the distortion light comes on then back down until it goes out. Pretty straightforward right? Now, throw in a DSP. What I am finding is that the lower the input sensitivity I pick for example 1v the more the input clips. The higher it is for example something like 4v or 5.6v the less the input clips or there isn’t any clipping at all. But then you measure the voltage at the output section of the dsp the higher the number at the input side, the less voltage comes out of the dsp output, so when you move to the amp to set the final gain stage, you are having to turn the gain up more and thus inducing floor noise into the signal. Tell me if I’m doing something wrong here please? 😊


I'm not following where you feel the problem is? You feel that winding more gain in on the power amp input is degrading the chain through bringing the noise floor up?


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## Holmz (Jul 12, 2017)

Are there options on the output gain?
I see that on the last page that they are set to zero, but do they go both ways?


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## sfarisminhas (Apr 4, 2019)

Muu said:


> I'm not following where you feel the problem is? You feel that winding more gain in on the power amp input is degrading the chain through bringing the noise floor up?


At the DSP you have a range of input sensitivity settings that start at something like 240mv and go up to 7.2v with ranges in between. The lower the number I go, the more clipping at the input and output I see. The higher I go the cleaner the signal, but then when I measure the voltage the less voltage comes out, which in turn means that the gain needs to be increased on the amp. Thus increasing noise.


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## jheat2500 (Mar 1, 2021)

Match the input of the dsp to the output of the source unit so there is no clipping. From there you have to set your gains on your amplifier(s) accordingly.


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## Muu (Jan 22, 2020)

sfarisminhas said:


> At the DSP you have a range of input sensitivity settings that start at something like 240mv and go up to 7.2v with ranges in between. The lower the number I go, the more clipping at the input and output I see. The higher I go the cleaner the signal, but then when I measure the voltage the less voltage comes out, which in turn means that the gain needs to be increased on the amp. Thus increasing noise.


I think you're getting overly obsessed with lifting the noise floor on the input stage of your power amps. If you're hearing a large amount of noise, check your wiring first before over driving the DSP.

Digitally clipping a signal at your DSP input will always sound nasty, squaring off the sine with all the ringing and harmonics that brings.

I did my honours degree in audio engineering and my lecturers used to say:
"Audio signals are like jumping on a trampoline, analogue clipping is like jumping too high and bumping the ceiling in that it hurts but you'll come down largely in the same shape you went up, digital clipping is like jumping under a helicopter"

You want to avoid that helicopter at all costs, in a broadcast space we leave 9dB of signal headroom.


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## sfarisminhas (Apr 4, 2019)

Hi. That sounds fine. Basing on the fact that my HU has a 5v preout, I guess that would mean setting the DSP input stage at 5.6v or whatever it is. The pre-EQ and level trims are okay at 0db yes?


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## Muu (Jan 22, 2020)

Yeah that's where I'd be setting the input pots, that way the theory is that even when the HU is at max you still have some DSP headroom.


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## sfarisminhas (Apr 4, 2019)

I see, so basically I’ll initially check the voltage coming out of the HU at full undistorted volume.


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## sfarisminhas (Apr 4, 2019)

It’s a 5v pre-out. I think it clips at volume 49, but I need to double check this.


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## sfarisminhas (Apr 4, 2019)

Muu said:


> Yeah that's where I'd be setting the input pots, that way the theory is that even when the HU is at max you still have some DSP headroom.


The level trim and the pre-EQ trim are okay where they are correct?


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## Muu (Jan 22, 2020)

sfarisminhas said:


> The level trim and the pre-EQ trim are okay where they are correct?


If you have some headroom then yes


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## Slayerx (Jul 2, 2021)

I know this is an old thread but I was just setting up my twk and setting input sensitivity and the highest I can go without it going into the red is 350mV. 
I also noticed on the output section that the tun software automatically set all the output levels to -12db why would it do that ?

My rca's come off of my front speaker wires with a special made harness for bmw hifi system so I have no idea what my headunit output voltage is from the rca's.

My amp gains are turned up about alittle more then half way and were set by DMM to 17.3 volts for front and rear using 1000hz sine wave and underseat mid bass woofers to the same voltage using 5000hz sine wave and amp is jl audio xd600/6v2


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## sageRJ (Jun 26, 2021)

Dead thread incoming! I’m probably reading too much into this but I have a similar question. My Pioneer states 4v preout. My Helix M Four DSP has no external gain, the input sensitivity is done in software. I choose RCA instead of High Level and my choices are 1v up to 4v with 0.6v intervals. Initially I set to 4 and called it a day.

Instead of trusting Pioneer implicitly, should I instead measure line level output voltage from the RCA manually and setting the DSP at say 3.4 or 2.8 if that’s what it’s closer to?


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## 156546 (Feb 10, 2017)

set the input sensitivity of the DSP so that it can never be clipped by the incoming signal. Never. If your head unit is 4V, set the DSP at 5V. The "resolution" thing is meaningless (for the most part). Then, make sure your DSP doesn't clip on the output. Leave room. Then, raise the gains on the amplifiers until the amps distort or the system is loud enough to satisfy you. 

All of this pushing for the Nth degree of optimization and headroom and mumbo jumbo is silly.


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## sageRJ (Jun 26, 2021)

Thank you for the advice. The only way to get up to 5V is to switch over to "High Level" as seen in the second picture. So, hopefully, that is simply a label designation to allow for higher input Voltage. So regardless that I'm not using high level input, I'm going to select that, set to 5V, then check for no output clipping. Could I try at 4V and see if there's not clipping at max volume? Or would you say stick with 5V period.

This is a DSP/Amplifier in one so I assume there's no further gain/sensitivity adjustment to be done here. Subsequently I'll set the gain correctly on the next amp in line for the subwoofer.


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## 156546 (Feb 10, 2017)

Right. Switch to high level.

Don't use the sine wave and the 3/4 volume control process.


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## sageRJ (Jun 26, 2021)

I’m using a DD-1 to determine max HU volume and output clipping from the DSP/Amp and second mono amp.


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## Holmz (Jul 12, 2017)

sageRJ said:


> I’m using a DD-1 to determine max HU volume and output clipping from the DSP/Amp and second mono amp.


Is that better than using a power resistor and a scope or DMM?


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## 156546 (Feb 10, 2017)

sageRJ said:


> I’m using a DD-1 to determine max HU volume and output clipping from the DSP/Amp and second mono amp.


Unless you plan to NEVER turn the volume up past that point and you think you can carefully assess the maximum level in the music, this is the wrong way to do it. The point here is not to set the input sensitivity of the DSP for the max UNCLIPPED volume, it's to set it so it doesn't clip at the MAX volume. This is especially important if you aren't the one who will be listening to the system. For retail installers this is really important because DIGITAL clipping sounds like broken speakers.

In the DSP, the max is 0dB, unless the designer has set the 0db spots on the level controls below actual 0db. If the inputs are maxed and the outputs are maxed, then your EQ cannot include a boost above 0 at any frequency at which the recorded level may reach 0dB. This is most likely going to be in the bass and clipping the A/D or the beginning of the digital chain won't provide a bunch of distortion in the sub, it'll happen much higher--midrange frequencies or even tweeters. 

All of this maxing out s**t is not the way in a digital system.


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## sageRJ (Jun 26, 2021)

This explanation is helping me understand your article more as well. “A scope and a sine wave or a DD-1 is not a substitute for reading the manual and understanding what it indicates. And it’s important there IS a suitable manual for a DSP.”

This is entirety of what the Helix manual states on DSP input sensitivity.


> Adjustment of the input sensitivity Attention: It is mandatory to properly adapt the input sensitivity of the M FOUR DSP to the signal source in order to avoid damage to the amplifier.
> If you want to change the input sensitivity use the “Input Gain” menu of the DSP PC-Tool soft- ware.
> The factory setting of the input sensitivity is 20 Volts for the Highlevel and 4 Volts for the lowlevel Line Inputs. Only if the head unit / car radio doesn ́t deliver enough output level, the input sensitivity should be increased carefully.





GotFrogs said:


> Unless you plan to NEVER turn the volume up past that point


I won’t. I thought that was the point.


GotFrogs said:


> and you think you can carefully assess the maximum level in the music


I thought that was the point of using a loud test tone. You know music will generally never go above that.

Why wouldn’t I want to use the DD-1 to determine that max HU volume? That signal is still analog before it reaches the DSP. Wouldn't I not want the potential to start with a clipped source?

I understand what you’re saying about this being a digital environment otherwise. HU is 4V, great, set the DSP gain to 5V for some headroom and call it a day. At that point it’s fine to use the DD-1 to confirm no clipping at the DSP speaker outputs, correct? (remember it’s an amplifier as well)

Disclaimer: in no way trying to challenge anything you’re saying. I want to understand this conceptually and can only get there by flushing out the disconnects in my thought processes.


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## 156546 (Feb 10, 2017)

The concept is really easy. For digital, we want to err on the side of preventing digital clipping rather than on the side of maximizing signal. In an analog system, a little clipping isn't audible. In a digital system, a little digital clipping sounds terrible.

So, find out the point at which the radio clips. Then, find the highest possible signal voltage from the radio and set the DSP input sensitivity there.

If you have an aftermarket radio, then a 1k test tone is fine if you never boost the bass or the treble. If you have a factory head unit or amp as a source, then you have to measure the frequency response FIRST to figure out which frequency is the loudest and then use a sine wave at 0dB at that frequency.


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## sageRJ (Jun 26, 2021)

Understood. DD-1 with a 1 kHz tone to find max aftermarket head unit volume is fine. I'll use 0 dB because much of the music I listen to is slammed with a brick wall limiter with only -0.03 dB of headroom at the loudest points. And the major streaming services compress it to -14 LUFS.

See what kind of Voltage I'm getting there. Confirm it's well under 4V and if it isn't bump it up to 5V on the DSP.

Tune the system. If anything gets boosted, I'll recheck Voltages and adjust DSP input gain/sensitivity accordingly.


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## sageRJ (Jun 26, 2021)

I'm going to leave this here for others that come across this thread. I had read this previously but re-reading it now after the last few replies here has helped it fully sink in.


> Andy's tech for today:
> Settings gains with a DSP.
> 
> After tech supporting someone yesterday, it occurred to me that this process may require a little explanation because it's a little more complicated than the standard process we're all used to using with analog gear.
> ...


This is my particular head unit; Pioneer DMH-WT8600NEX @ 20:13

At full volume, pre-outs output 3.64V @ 1kHz and 4.65V @ 40Hz. You were right on the money with 5V input sensitivity on the DSP. So with an aftermarket HU rated at 4V and the Helix factory set to RCA input gain at 4V, there is a very good chance for clipping the ADC in the lower frequencies before the signal was even processed.


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## Holmz (Jul 12, 2017)

sageRJ said:


> I'm going to leave this here for others that come across this thread. I had read this previously but re-reading it now after the last few replies here has helped it fully sink in.
> 
> This is my particular head unit; Pioneer DMH-WT8600NEX @ 20:13
> 
> At full volume, pre-outs output 3.64V @ 1kHz and 4.65V @ 40Hz. You were right on the money with 5V input sensitivity on the DSP. So with an aftermarket HU rated at 4V and the Helix factory set to RCA input gain at 4V, there is a very good chance for clipping the ADC in the lower frequencies before the signal was even processed.


How can that be?
Were they both using 0dBfs?

Maybe using a DMM could get varying frequencies, or some bass boost is happening.
(I would probably check at 20, 80 and160 as well)

Thst also sort of confirms Andy’s remark about being on th hairy edge and then adding some extra bass or treble knob and throwing the clipping into a hissying fit.


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## 156546 (Feb 10, 2017)

Holmz said:


> How can that be?
> Were they both using 0dBfs?
> 
> Maybe using a DMM could get varying frequencies, or some bass boost is happening.
> ...


Just hook the output of the radio up to the input of a sound card and measure this with REW, Then, choose the frequency at which the level is highest to measure the voltage. A true RMS VOM is kind of necessary here.


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## THX0849 (Sep 24, 2019)

REW can be used as an electrical RTA not just via microphone?

Sent from my Pixel 2 using Tapatalk


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## 156546 (Feb 10, 2017)

THX0849 said:


> REW can be used as an electrical RTA not just via microphone?
> 
> Sent from my Pixel 2 using Tapatalk


Of course. It doesn't know the difference. You just need to get the signal in there via a soundcard,


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## Holmz (Jul 12, 2017)

Via an 1/8” microphone input…


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## THX0849 (Sep 24, 2019)

Mind blown

Sent from my Pixel 2 using Tapatalk


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## 156546 (Feb 10, 2017)

Holmz said:


> Via an 1/8” microphone input…


Or you can puck up an Art USB dual pre or a behringer or some other USB audio interface with a balanced input and a simple attenuator. I do this all the time.


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## Holmz (Jul 12, 2017)

We actually hooked up an engine’s ”Crank Index Position” (CRIP) sensor to the left channel.
The engine had another position sensor on theother end of the crank to alarm when crank was under going bad torsion flex.
So we put that one into the right hand channel.

The only thing that matters is keeping the input voltage within the mic’s voltage limits.

And ”bingo” one has digitised 2 channel data (of anything) at 44.1 k-samples/sec.


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## sageRJ (Jun 26, 2021)

GotFrogs said:


> set the input sensitivity of the DSP so that it can never be clipped by the incoming signal. Never. If your head unit is 4V, set the DSP at 5V. The "resolution" thing is meaningless (for the most part). Then, make sure your DSP doesn't clip on the output. Leave room. Then, raise the gains on the amplifiers until the amps distort or the system is loud enough to satisfy you.
> 
> All of this pushing for the Nth degree of optimization and headroom and mumbo jumbo is silly.


I can only speak to the Helix M Four DSP with certainty but switching the gain in software over to High Level to access 5V and above results in no input signal to the DSP. I confirmed this using the Input Signal Analyzer tool within the software. Switching it back to RCA shows the full range signal again. My assumption is switching to High Level in the software causes the DSP to ignore incoming RCA signal and only look at the High Level input.

Unless someone knows more about the DSP PC-Tool software, it appears the only choice with RCA input is to choose 4Vrms and cross your fingers the source never clips at the input.


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