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

[Canar]

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.

I have a question that's marginally off-topic, but this post triggered all my keyword detectors. Windowed sinc is symmetric. What would similar functions be in the asymmetric case? The symmetric, acausal nature of sinc has always bugged me, but I've never found a reference containing asymmetric, causal analogues that I could use in SRC contexts.