# CarPC and USB DAC ?



## t3sn4f2 (Jan 3, 2007)

Do the excellent S/N ratio and dynamic range specs on a high end USB DAC like an Apogee Mini-DAC apply when playing back regular CD audio tracks of 16bit/44kHz format or are those measured specs only for the high resolution formats. Also does anyone know if you can output DRM'd music threw the analog output of a USB DAC like the Apogee?


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## felix509 (Dec 17, 2006)

One of the main advantages of the USB DAC is taking the spinning CD transport and it's associated timing errors or 'Jitter' out of the signal path, so my suggestion would be to rip the CD you want to listen to to your hard drive in a lossless format, then play it back through the USB DAC straight from the hard drive. 

But to answer your question, I would expect the miniDAC playback specs would apply to CDs as well as ripped music.


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## t3sn4f2 (Jan 3, 2007)

felix509 said:


> One of the main advantages of the USB DAC is taking the spinning CD transport and it's associated timing errors or 'Jitter' out of the signal path, so my suggestion would be to rip the CD you want to listen to to your hard drive in a lossless format, then play it back through the USB DAC straight from the hard drive.
> 
> But to answer your question, I would expect the miniDAC playback specs would apply to CDs as well as ripped music.


Thanks but I am looking to get the best mp3 sound I can. Mp3s are good enough to be acceptable to me in a car but the noise or hiss from a low quality low voltage line out on a portable mp3 player or plain sound card are my concern. When I look at excellent noise specs they aren't sampled at the same bit rate and frequency as a CD format file so I'm not exactly sure what that means. The recorded rate? The playback rate? I'm totally confused how that works. From RMAA results, I've seen that the ratings for a high end DAC go down to the level of a much less expensive soundcard when test state "Sampling mode: 16-bit, 44 kHz
".


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## t3sn4f2 (Jan 3, 2007)

Lets bump this up and see if anyone bites.........


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## durwood (Mar 7, 2007)

Well Felix uses a DAC I believe for his carpc, but it's not the one you have listed. There are plenty of specs that can easily get confusing. 

One of the biggest reasons as Felix stated was to reduce Clock Jitter. However, there are Non-oversampled (NOS) dacs (no IMD) vs Re-sampled dacs that increase the frequency response but might increase IMD.

Maximum signal to noise ratio on 16bit is 96db (that is a mathmatic limitation), 24bit increases this to a possible maximum of 144dB. It's about 6db per bit. So if you can playback in 24bit, then the limiting factor will be the opamps and the d/a conversion. The question is then, does 24bit sound better for something that is recorded in 16bit? I'm not sure. I will have to think about it.

Also, if it is resampled to a higher bitrate i.e. 96khz, your usable frequency range increase to 48khz (Nyquist sampling theorem-1/2 your sampling frequency), but there exists possiblity for Intermodulation Distortion (IMD) if not done correctly-this is from rounding errors. Of another note, most DSP processors do all the mathmatical computations at 32 bit (inside a soundcard), so it does not introduce noise.

A quick google for you found this (although it is geared more towards recording). I haven't done anything with DSP since I left school, so I am in no way an expert.


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## durwood (Mar 7, 2007)

A recent discussion about DAC's and how to determine their worthiness...and at mp3car of all places.

More about Dacs

The mother of all DAC lists as far as I know


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## t3sn4f2 (Jan 3, 2007)

durwood said:


> A recent discussion about DAC's and how to determine their worthiness...and at mp3car of all places.
> 
> More about Dacs
> 
> The mother of all DAC lists as far as I know


Thanks Durwood, i'll read up.


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