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Old 2nd February 2004, 07:09 PM   #1
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Default USB DACs again

OK so I put together a good-quality DAC (PCM2707>>TDA1543)driven off the USB port on my PC. Is there an advantage to copying my CDs to the hard drive of my computer then replaying from there, or do I get the same quality by simply playing them on the computer's CDROM and stuffing the data out as USB Audio? The PCM2707 generates its own I2S low-jitter clock, so I would think that the source feeding the USB port should not really matter.....
Adam
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Old 2nd February 2004, 09:02 PM   #2
macboy is offline macboy  Canada
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What will matter is the sample rate. Most PC audio operates at the de-facto standard of 48 kHz. This means that 44.1 kHz CD audio gets resampled. You don't want that. In addition to ensuring that the interface operates at 44.1 kHz, you need to make sure to bypass the kmixer. This is the windows component that controls volume, mixes all the different sounds together (wav playback with system sounds etc.). This is known to adversely affect the sound quality. If you would like to delve into these issues further, check out the home theatre PC forum over at www.avsforum.com .
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Old 3rd February 2004, 11:55 PM   #3
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Default bit rate

I had an exchange with Gordon at Wavelength Audio yesterday about this. He recommends using Apple's (free!) music player, which allows setup of the playback bit rate. The USB Audio device tells the software what bit rates it is capable of accepting (for the PCM27XX it's 32, 44.1, or 48kHz). Whether playback is from CDROM or hard drive, the data is buffered by RAM before being spit out to the USB audio device.

This is very cool guys--it means we have a way to transfer digital data out with very low jitter and with platform independence--MAC, PC, whatever, doesn't matter at all!

cheers
Adam
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Old 4th February 2004, 03:47 PM   #4
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You are not talking about QuickTime player I hope. I really hate it.

If you install it, then is it in your taskbar at three places, on your desktop, in your startmenu. It's QuickTime everywhere. bwah .
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Old 4th February 2004, 07:15 PM   #5
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Default players

Nope, Gordon recommended I-Tunes, the player software for the I-Pod. Available free for both Win and Mac.

**FLASH**--I just checked out Gordon's website again here:

http://www.wavelengthaudio.com/Cosecant.html

He's added a whole bunch of detail on how-to and what works. Extremely cool!

Adam
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Old 5th February 2004, 07:00 AM   #6
MWP is offline MWP  Australia
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Quote:
Originally posted by macboy
What will matter is the sample rate. Most PC audio operates at the de-facto standard of 48 kHz.
This is wrong.

The "standard" for PC audio is 44.1khz, no different from CD audio.

What you are talking about is the avg consumer sound-cards upsampling to 48Khz on the card... this is done to the AC97 standard to be compatible with DATs.

The PCM2707 like the PCM2902 that im using, does not do any internal resampling... so if you play audio off a CD at 44.1Khz, itll come out of the PCM2707 at 44.1Khz.
So.... nothing to worry about here.

Eeek... dont use any Apple software.
If you want quality avoid that kind of software.

First use EAC (ExactAudioCopy is freeware) to rip the CD to your HDD in the desired format (a lossless format or OGG vorbis are best).

Then play back the audio with Foobar2000 (again, freeware).

Itll take more time on your part to use both of these, but youll get much better results.

Details on the USB+DAC i built are here:
http://www.overclockers.com.au/~mwp/dac3/
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