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Sample rate conversion
MannyCalavera
post Apr 11 2011, 18:50
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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 biggrin.gif

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.
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Axon
post Apr 12 2011, 20:09
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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.
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2Bdecided
post Apr 13 2011, 15:21
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QUOTE (Axon @ Apr 12 2011, 20:09) *
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.
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Axon
post Apr 13 2011, 22:43
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QUOTE (2Bdecided @ Apr 13 2011, 09:21) *
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? smile.gif

This post has been edited by Axon: Apr 13 2011, 22:48
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Canar
post Apr 14 2011, 00:03
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QUOTE (Axon @ Apr 13 2011, 14:43) *
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.


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Posts in this topic
- MannyCalavera   Sample rate conversion   Apr 11 2011, 18:50
- - saratoga   QUOTE (MannyCalavera @ Apr 11 2011, 13:50...   Apr 11 2011, 18:58
- - Arnold B. Krueger   QUOTE (MannyCalavera @ Apr 11 2011, 13:50...   Apr 12 2011, 14:29
- - Axon   If you are just mixing, then you ought to be able ...   Apr 12 2011, 20:09
|- - 2Bdecided   QUOTE (Axon @ Apr 12 2011, 20:09) If the ...   Apr 13 2011, 15:21
|- - Axon   QUOTE (2Bdecided @ Apr 13 2011, 09:21) Th...   Apr 13 2011, 22:43
|- - Canar   QUOTE (Axon @ Apr 13 2011, 14:43) I think...   Apr 14 2011, 00:03
|- - Axon   QUOTE (Canar @ Apr 13 2011, 18:03) QUOTE ...   Apr 14 2011, 03:26
- - Wombat   QUOTE (2Bdecided @ Apr 13 2011, 15:21) Yo...   Apr 13 2011, 16:05
|- - bandpass   Given 10 seconds of 440Hz tone and upsampling from...   Apr 13 2011, 20:25
|- - Wombat   QUOTE (bandpass @ Apr 13 2011, 20:25) Giv...   Apr 13 2011, 20:47
|- - bandpass   QUOTE This must be lowpassed already even if i don...   Apr 13 2011, 21:19
- - Wombat   I admit i have no clue about some things you talk ...   Apr 14 2011, 00:44
|- - Canar   QUOTE (Wombat @ Apr 13 2011, 16:44) I adm...   Apr 14 2011, 00:52
||- - Wombat   QUOTE (Canar @ Apr 14 2011, 00:52) Sample...   Apr 14 2011, 00:58
||- - Canar   QUOTE (Wombat @ Apr 13 2011, 16:58) Exact...   Apr 14 2011, 01:03
|- - saratoga   QUOTE (Wombat @ Apr 13 2011, 19:44) I adm...   Apr 14 2011, 01:03
- - Wombat   QUOTE (saratoga @ Apr 14 2011, 01:03) Alt...   Apr 14 2011, 01:11
|- - saratoga   QUOTE (Wombat @ Apr 13 2011, 20:11) QUOTE...   Apr 14 2011, 01:17
|- - bandpass   QUOTE (saratoga @ Apr 14 2011, 01:17) Obv...   Apr 14 2011, 07:30
|- - Axon   QUOTE (bandpass @ Apr 14 2011, 01:30) QUO...   Apr 14 2011, 19:38
|- - bandpass   QUOTE (Axon @ Apr 14 2011, 19:38) Strictl...   Apr 14 2011, 20:24
- - Wombat   QUOTE (bandpass @ Apr 14 2011, 20:24) aft...   Apr 14 2011, 20:46
|- - bandpass   QUOTE (Wombat @ Apr 14 2011, 20:46) I sti...   Apr 14 2011, 22:16
|- - Alexey Lukin   QUOTE (bandpass @ Apr 14 2011, 17:16) Bec...   Apr 14 2011, 22:26
|- - Wombat   QUOTE (bandpass @ Apr 14 2011, 22:16) Usi...   Apr 14 2011, 22:27
|- - bandpass   QUOTE (Alexey Lukin @ Apr 14 2011, 22:26)...   Apr 15 2011, 07:18
- - Alexey Lukin   48 -> 96 kHz conversion may leave signal sample...   Apr 14 2011, 21:35
- - Wombat   QUOTE (Alexey Lukin @ Apr 14 2011, 21:35)...   Apr 14 2011, 21:49
- - Wombat   I am getting slowly mad in here or lowpass myself ...   Apr 14 2011, 22:49
|- - bandpass   Okay, curiousity got the better of me: in the 48k ...   Apr 15 2011, 10:39
- - Wombat   Many thanks bandpass for your efforts. Very intere...   Apr 15 2011, 16:24
- - Alexey Lukin   I've just verified that SoX never preserves th...   Apr 15 2011, 17:10
- - Wombat   QUOTE (Alexey Lukin @ Apr 15 2011, 17:10)...   Apr 15 2011, 18:11
|- - bandpass   All I have told you is what I have observed throug...   Apr 15 2011, 22:17
- - Alexey Lukin   This is only due to the fact that you used the sin...   Apr 16 2011, 06:27
- - bandpass   QUOTE (Alexey Lukin @ Apr 16 2011, 06:27)...   Apr 16 2011, 08:41
- - Alexey Lukin   Agreed.   Apr 16 2011, 08:45


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