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Digitizing mono vinyl: using phase-inversion to reduce noise
alfienoakes101
post May 2 2007, 23:36
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Hi.

I have been using a long-winded process to reduce some extraneous noise when digitizing mono vinyl sources. With Sound Forge, I have been subtracting the difference between the two channels of my records, on the assumption that most of it is noise, and the resultant files are usually audibly better.

1. Invert the phase of one of the two channels on the original .wav file (1.wav).
2. Convert to mono by mixing the channels.
3. Save the difference (noise file) as a mono .wav file (2.wav).
4. Re-open the original "stereo" file (1.wav).
5. Convert to mono by mixing the two channels.
6. Save the sum as a mono .wav file (3.wav).
7. Open original "stereo" file (1.wav).
8. Open difference (noise) file (2.wav), copy it and overwrite onto left channel of 1.wav.
9. *edit* Invert noise channel.
10. Open sum file (3.wav), copy it and overwrite onto right channel of 1.wav.
11. Convert to mono by mixing the two channels.
12. Save changes to 1.wav.

Is there an audio editor that will allow me to subtract the difference of a stereo file in a single step, as it would save me a lot of time, and allow me to hear instantly whether the audio is significantly improved, without having to get confused by extra files? If I could work in flac, that would be even better.

If found the link below that references and old version of Cool Edit, but I gather that's been discontinued.

http://www.hydrogenaudio.org/forums/index....mp;#entry344060

Thanks.

This post has been edited by alfienoakes101: May 3 2007, 00:38
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bryant
post May 2 2007, 23:54
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When you mix the left and right channels to produce mono, that does essentially "subtract the difference" from the original file. After all, it's the "difference" that makes it stereo!

The procedure you describe will, I think, actually result in a mono file consisting of only one of the original channels. Your last step is to mix the sum and the difference which causes one channel to be cancelled out:

( (L + R) + (L - R) ) / 2 = L

The best thing would probably be to figure out which is the quietest of L, R, or (L + R) / 2 (mono mix) and use that. I don't think your long-winded scheme is achieving anything more than that.

edit: fix spelling

This post has been edited by bryant: May 2 2007, 23:55
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alfienoakes101
post May 3 2007, 01:16
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QUOTE (bryant @ May 2 2007, 23:54) *
Your last step is to mix the sum and the difference which causes one channel to be cancelled out:

( (L + R) + (L - R) ) / 2 = L


Err... you're right. Maths was never my strong point. I guess the "improvement" I was hearing was either my imagination, or the result of the remaining channel sounding better than the discarded one.

Nonetheless, is the principle of what I'm trying to do sound? That is, separating difference between the two mono tracks, and somehow using that to remove noise from the eventual true-mono audio. If so, is there software (preferably free/share-ware) that will do this for me in one or two simple steps?

Thanks.
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Posts in this topic
- alfienoakes101   Digitizing mono vinyl: using phase-inversion to reduce noise   May 2 2007, 23:36
- - bryant   When you mix the left and right channels to produc...   May 2 2007, 23:54
|- - alfienoakes101   QUOTE (bryant @ May 2 2007, 23:54) Your l...   May 3 2007, 01:16
- - AndyH-ha   There are two reasonable approaches. Which one to ...   May 3 2007, 00:25
|- - Wook   QUOTE (AndyH-ha @ May 2 2007, 23:25)...   May 3 2007, 10:05
- - pdq   The noise in the two channels can be highly correl...   May 3 2007, 12:19
|- - Wook   QUOTE (pdq @ May 3 2007, 11:19) The noise...   May 4 2007, 12:02
|- - pdq   QUOTE (Wook @ May 4 2007, 07:02) QUOTE (p...   May 4 2007, 16:51
- - Robbie   Certainly just summing the two channels will cance...   May 3 2007, 12:33
- - alfienoakes101   I guess then that the "noise" that I hav...   May 3 2007, 17:49
|- - bryant   QUOTE (alfienoakes101 @ May 3 2007, 09:49...   May 3 2007, 18:01
|- - pdq   QUOTE (bryant @ May 3 2007, 13:01) OT: Th...   May 3 2007, 20:05
|- - hushypushy   QUOTE (pdq @ May 3 2007, 12:05) QUOTE (br...   May 4 2007, 06:21
- - AndyH-ha   That cartridge alignment is (reasonably) correct h...   May 3 2007, 19:57
- - Axon   1. Sum and difference the L and R channels to get ...   May 4 2007, 06:46
- - AndyH-ha   1. Sum and difference the L and R channels to get ...   May 4 2007, 07:56
- - 2Bdecided   Back to removing noise from mono LPs: I've alw...   May 4 2007, 10:41
- - AndyH-ha   The best way to play a mono recording must be with...   May 4 2007, 19:45
- - 2Bdecided   I find... stereo > declick > decrackle ...   May 8 2007, 13:56
- - AndyH-ha   It's a trade-off. There is some advantage to m...   May 8 2007, 21:47
|- - cliveb   QUOTE (AndyH-ha @ May 8 2007, 21:47)...   May 9 2007, 08:40
- - AndyH-ha   The overall advantage is in declicking first. Howe...   May 9 2007, 23:38
|- - cliveb   QUOTE (AndyH-ha @ May 9 2007, 23:38)...   May 10 2007, 10:03
- - 2Bdecided   Rather than saying "it won't work", ...   May 10 2007, 10:36
|- - cliveb   QUOTE (2Bdecided @ May 10 2007, 10:36) My...   May 10 2007, 23:17
|- - cliveb   QUOTE (2Bdecided @ May 10 2007, 10:36) If...   May 11 2007, 09:51
|- - 2Bdecided   QUOTE (cliveb @ May 11 2007, 09:51) QUOTE...   May 14 2007, 10:34
|- - cliveb   QUOTE (2Bdecided @ May 14 2007, 10:34) Se...   May 14 2007, 12:30
- - AndyH-ha   Automated declicking is never the end of declickin...   May 10 2007, 19:58
- - AndyH-ha   I have a segment of that recording, declicked, tha...   May 11 2007, 05:44
|- - cliveb   QUOTE (AndyH-ha @ May 11 2007, 05:44...   May 11 2007, 08:48
|- - 2Bdecided   QUOTE (AndyH-ha @ May 11 2007, 05:44...   May 14 2007, 11:35
- - AndyH-ha   No, there is no such box. Does its existence depen...   May 11 2007, 19:35
|- - woody_woodward   QUOTE (AndyH-ha @ May 11 2007, 11:35...   May 11 2007, 21:50
|- - cliveb   QUOTE (woody_woodward @ May 11 2007, 21:5...   May 12 2007, 10:41
- - charliemcdo   Sorry to be off topic here, but I just wanted to a...   May 12 2007, 18:02
- - AndyH-ha   Obviously, the file attachment section is a privil...   May 12 2007, 19:19
|- - cliveb   QUOTE (AndyH-ha @ May 12 2007, 19:19...   May 12 2007, 22:51
- - AndyH-ha   And do you perchance remember a late night visit f...   May 13 2007, 05:20
- - 2Bdecided   I bet it's something to do with developers or ...   May 14 2007, 09:55
- - 2Bdecided   Hi Clive, I wasn't criticising or complaining...   May 14 2007, 13:21
|- - cliveb   QUOTE (2Bdecided @ May 14 2007, 13:21) I ...   May 14 2007, 14:50
- - AndyH-ha   The file, resampled to 16 bit, is at http://www.hy...   May 15 2007, 08:43
|- - 2Bdecided   QUOTE (AndyH-ha @ May 15 2007, 08:43...   May 18 2007, 10:04
- - AndyH-ha   Do you want something from another album to play w...   May 20 2007, 00:42


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