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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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Wombat
post Apr 14 2011, 00:44
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I admit i have no clue about some things you talk but to summarize my findings i still donīt see anyone convincing me there is upsampling without lowpassing, so changing EVERY single musical bit in the process.

On http://en.wikipedia.org/wiki/Upsampling they talk about the 2 ways of implementing
1. Add zeros between each sample -> to my understanding all resamplers do
2. Filter with a low-pass filter which, theoretically, should be the sinc filter -> that no resampler does because, also from Wikipedia:

"The second step calls for the use of a perfect low-pass filter, which is not implementable"
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Canar
post Apr 14 2011, 00:52
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QUOTE (Wombat @ Apr 13 2011, 16:44) *
I admit i have no clue about some things you talk but to summarize my findings i still donīt see anyone convincing me there is upsampling without lowpassing, so changing EVERY single musical bit in the process.
Sample-and-hold, ie. "nearest neighbour", ie. out[2*x]=in[x];out[2*x+1]=in[x] is trivial upsampling without lowpassing, though it's gonna generate a lot of high-frequency aliasing. Solution? Low-pass the aliasing out.

I suspect that's why step 2 exists in your algorithm. Step 1 will resample (even accurately) but the issue becomes high-frequency aliasing, ie. putting high-frequency content in the signal that was not there originally.

This post has been edited by Canar: Apr 14 2011, 00:54


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Wombat
post Apr 14 2011, 00:58
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QUOTE (Canar @ Apr 14 2011, 00:52) *
Sample-and-hold, ie. "nearest neighbour", ie. out[2*x]=in[x];out[2*x+1]=in[x] is trivial upsampling without lowpassing, though it's gonna generate a lot of high-frequency aliasing. Solution? Low-pass the aliasing out.

Exactly, that aliasing i mentioend in post 6 above. We are running in circles smile.gif

This post has been edited by Wombat: Apr 14 2011, 00:59
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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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