IPB

Welcome Guest ( Log In | Register )

Digitizing mono vinyl: using phase-inversion to reduce noise
alfienoakes101
post May 2 2007, 23:36
Post #1





Group: Members
Posts: 26
Joined: 10-March 06
Member No.: 28381



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
Go to the top of the page
+Quote Post
 
Start new topic
Replies
2Bdecided
post May 10 2007, 10:36
Post #2


ReplayGain developer


Group: Developer
Posts: 5089
Joined: 5-November 01
From: Yorkshire, UK
Member No.: 409



Rather than saying "it won't work", do you think either of you can try the foobar2k keep centre channel plug-in? Or post an audio extract I can test it with?


My home audio set up is currently in pieces, and I don't have a "mono record, recorded in stereo, declicked and decrackled, but not yet converted back to mono" to test.

From simulation (mixing in run-in groove noise and clicks with various panning), it seems that this plug-in does offer some advantage to a plain old "sum both channels" at the end of the job, but I suspect with a real recording and all its vagaries this advantage could reduce dramatically.


If you can test a real recording in foobar2k, or upload a 30 second extract of a mono restoration, just before the final mixdown to mono, so I can test it myself, that would be great.

If I do test, I'll upload my results for all to hear, but I need some source material!

Cheers,
David.

(I'm ashamed I haven't got a single archived track to test this on, but I have never saved the result at this stage!)

This post has been edited by 2Bdecided: May 10 2007, 11:58
Go to the top of the page
+Quote Post
cliveb
post May 11 2007, 09:51
Post #3


WaveRepair developer


Group: Developer
Posts: 838
Joined: 28-July 04
Member No.: 15845



QUOTE (2Bdecided @ May 10 2007, 10:36) *
If you can test a real recording in foobar2k, or upload a 30 second extract of a mono restoration, just before the final mixdown to mono, so I can test it myself, that would be great.

OK, I fished around in the attic and did find a few mono records, so I've recorded a short section from one for you to play with. (If you're interested, it's an extract from Mozart's Flute Concerto No 2. Recording was made in 1958). Bear in mind that this is a straight recording - I haven't done any declicking/denoising at all. My understanding is that your goal is to compare the effect on background noise of a straight mixdown to mono against Foobar's "keep centre channel" plugin, so I'd have thought the fact that this hasn't been declicked shouldn't affect the outcome of that. I deliberately picked a quiet section so that the surface noise is very obvious.

Attached File  mozart.flac ( 1.26MB ) Number of downloads: 182
Go to the top of the page
+Quote Post
2Bdecided
post May 14 2007, 10:34
Post #4


ReplayGain developer


Group: Developer
Posts: 5089
Joined: 5-November 01
From: Yorkshire, UK
Member No.: 409



QUOTE (cliveb @ May 11 2007, 09:51) *
QUOTE (2Bdecided @ May 10 2007, 10:36) *
If you can test a real recording in foobar2k, or upload a 30 second extract of a mono restoration, just before the final mixdown to mono, so I can test it myself, that would be great.

OK, I fished around in the attic and did find a few mono records, so I've recorded a short section from one for you to play with. (If you're interested, it's an extract from Mozart's Flute Concerto No 2. Recording was made in 1958). Bear in mind that this is a straight recording - I haven't done any declicking/denoising at all. My understanding is that your goal is to compare the effect on background noise of a straight mixdown to mono against Foobar's "keep centre channel" plugin, so I'd have thought the fact that this hasn't been declicked shouldn't affect the outcome of that. I deliberately picked a quiet section so that the surface noise is very obvious.

Attached File  mozart.flac ( 1.26MB ) Number of downloads: 182



Thanks Clive, that's perfect. That background noise is just the kind of thing I was hoping to test.

Unfortunately, my testing was more complicated than I expected! (Though the results are encouraging).

Firstly, I'd already spotted that there's some kind of bug/feature/issue which reduces the amount of treble in the "keep centre" output of this plug-in. Therefore, for a "fair" test, I had to EQ the result to make it sound more like the original. I've also provided the output before my EQing.

Secondly, though there is distinctive background noise in this extract, there are also some clicks. These can be distracting when comparing, so I've also done a version with the clicks removed. I used Cool Edit Pro's Click/Pop/Crackle Eliminator with the "Old Record - Quiet Audio" pre-set. I didn't tweak it at all (I didn't even autofind all levels) so it's not a good declicking job - just for testing.


So, here are the results. You don't need to download all these files - I've just included them all for reference.

Attached File  1_Flute_Concerto_2_original_mono.flac ( 757.87K ) Number of downloads: 180
1 is Clive's original, converted to mono by summing the channels.

Attached File  2_Flute_Concerto_2_original_centre_cut.flac ( 686.01K ) Number of downloads: 176
2 is Clive's original, converted to mono using the Centre Cut plug-in

Attached File  3_Flute_Concerto_2_original_centre_cut_EQ.flac ( 750.42K ) Number of downloads: 174
3 is file 2 (Centre Cut) EQ'd by me


Attached File  4_Flute_Concerto_2_declick.flac ( 1.33MB ) Number of downloads: 179
4 is Clive's original, declicked by me

Attached File  5_Flute_Concerto_2_declick_mono.flac ( 754.56K ) Number of downloads: 174
5 is file 4 (declicked), converted to mono by summing the channels.

Attached File  6_Flute_Concerto_2_declick_centre_cut.flac ( 681.18K ) Number of downloads: 176
6 is file 4 (declicked), converted to mono using the Centre Cut plug-in

Attached File  7_Flute_Concerto_2_declick_centre_cut_EQ.flac ( 745.48K ) Number of downloads: 177
7 is file 6 (declicked, Cenre Cut), EQ'd by me


Comparing file 3 with file 1, I find the remaining clicks too distracting to judge easily.

Comparing file 7 with file 5, I think the Centre Cut version has somewhat lower background noise, no appreciable artefacts from the Centre Cut processing, other than the EQ which I'm not sure I've corrected completely.


To me, this seems like a useful tool which I will add to my list of processes which I might choose to use, or at least try, depending on circumstances.

Hope this is of interest.


EDIT: what I didn't include, though it's easy enough to try, is just keeping the channel with the lowest noise from the two stereo channels. In this case, it's not as good as Centre Cut mono.

Cheers,
David.

This post has been edited by 2Bdecided: May 14 2007, 11:56
Go to the top of the page
+Quote Post

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


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 20th August 2014 - 12:12