Topic: Soundcard... Bit Perfect... ???... Questions...

[Swampy]

Okay, so I should probably know the answer to this, but I don't. I think I knew about this stuff when I was doing DAT transfers four years ago, but I promptly forgot it all when I went to JB3... I'm doing some cassette transfers with an ad1k into my Lexicon Omega. Does it matter if the soundcard (omega) is bit perfect on its spdif in? Does that only matter with a pre-recorded (ie dat) source, or do I need to worry about this doing a real-time transfer (cassette deck > 1k > Omega > Sonar). I tried to look up how to test, but didn't really come up with anything. Could anyone give me some guidance... Thanks!

[Craig T]

if you are recording a digital source (DAT, ad1k, etc), it is best to do so with a bit perfect soundcard.

[Swampy]

ok, right. So how do I test that? (I have a few different cards to choose from...)

[live2496]

The question is then, does the soundcard resample?

One way to tell is to generate low frequency square waves in software. Play it and capture it with the digital input of your dat.

Then go the other way. Playback the dat and capture the audio with the soundcard. Zoom in to the waveforms with audio software. If the waves are perfectly square, then no resampling has occurred. If the top of the wave is swaybacked then resampling has occurred.

You can also do bit for bit comparisons of the files, or put the waves out of phase and sum them. But this is is the simplest test I can think of using a dat, digital soundcard and some audio software.

[live2496]

To illustrate what to expect in a resampled wavefile, I have prepared a screenshot.



I used 40 Hz rectangular waves generated in Samplitude.
They were resampled to 88.2kHz using R8Brain which is a very good resampling program.

In the background we see the resampled file. Expect similar results if your soundcard resamples a digital source.

***************** warning ********************
*  Don't listen to these files except at very low levels.     *
*  When dealing with these types of files, or sine waves  *
*  turn your speakers off or monitor at a very low level.   *
********************************************