Sample rate conversion Options

[MannyCalavera]

Hello everyone.

I have a question regarding sample rate conversion algorightms.
I don't know how they work, but I guess you guys are more familiar with this

Let's say I have a 48 kHz wave file that I want to use in something I have to mix
with some 96 kHz material at certain places. This requires the 48 kHz file be resampled
and in the end back to 48.

So in short: does resampling 48 --> 96 --> 48 change the original or can the original
be restored 100% ?

I'm using Wavelab for this.

[Axon]

If you are just mixing, then you ought to be able to get the same results (to within -144db or better) by resampling the 96k content down to 48k, and mixing at 48k. The reason is that mixing is a purely linear operation.

48k->96k, being a 2x oversample, is among the most numerically conservative resampling possibilities. If the resampler is correctly implemented, 50% of all the samples should be numerically exact, with zero quantization error.

[2Bdecided]

If the resampler is correctly implemented, 50% of all the samples should be numerically exact, with zero quantization error.

That's an interesting use of the word "correctly" - a 2x resampler can easily be (and often is) perfect in terms of frequency and phase response, while giving 100% "new" samples.

You can easily design it to do as you suggest, but that's not necessarily the way all are designed.

Cheers,
David.

[Axon]

That's an interesting use of the word "correctly" - a 2x resampler can easily be (and often is) perfect in terms of frequency and phase response, while giving 100% "new" samples.

You can easily design it to do as you suggest, but that's not necessarily the way all are designed.

Feh. Yes, you are correct. Thanks for the catch.

I think that if I restrict my statement to the domain of windowed sinc filters, it's accurate. But any filter possessing an asymmetric response around the -6db point at Fs/2 is categorically not in that domain. While asymmetric filters are 2x more complex to implement, obviously they exist, particularly in software implementations where the symmetric optimization may not get performed. (offhand, I can't recall any specific instance of such a filter, but I am quite sure they exist.)

... Right?

This post has been edited by Axon: Apr 13 2011, 22:48