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Digitizing mono vinyl source, how is stereo -> mono done?
singaiya
post Nov 22 2005, 04:02
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I recently digitized a mono record, but am now realizing that in SoundForge 4.5 I recorded it as a stereo wav file. Ok, no biggie, I'll convert it to mono in the program. But then I noticed that the channels were actually quite different sounding. There are three different options for converting to mono in Soundforge, one of them allowing channel sliders to be moved as the output. On this record, the left channel sounded louder and brighter, the right channel was muffled and without much treble. So I used left one at about 70% and reduced the right to about 40%, which kept the overall peak about the same as before.

But this led me to wonder: if I had set the program to record in mono in the first place, how would it convert the "stereo" signal it receives from the soundcard? I presume it depends on the recording/editing software, but I don't know. When I previewed one of the other convert-to-mono settings (that was more "auto" and did not allow sliders) the sound was more muffled, presumably due to the right channel getting equal output as the left.

And another related question: have any of you noticed differences in channels with mono vinyl sources? I'm wondering if this is due to poor vinyl pressing, cartridge misalignment, or other.

This post has been edited by singaiya: Nov 22 2005, 04:35
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woody_woodward
post Nov 22 2005, 06:38
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Could be caused by misaligned cartridge. Stereo records record the left channel on the inner groove and the right channel on the outer groove. It is the outer groove wall that propells the stylus across the record. The right channel tends to wear more quickly. This can be exacerbated by a worn or misaligned stylus, also by heavy tracking presure. If the record is known to be mono and the right channle sounds muffled, I would be tempted to throw it away and use only the left channel.
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AndyH-ha
post Nov 22 2005, 07:51
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I've done quite a few old mono LPs and they all seemed to be cut properly. I like to use the Cool Edit Channel Mixer LR to Mid-Side preset set at 50/50 because its result shows both the summed to mono track and the out of phase noise that is removed by the process, but several different ways of converting to mono produce the same good mono track. The background noise is reduced about 3dB and very often a good part of the clicks, pops and crackle come out too.

Occasionally I have to choose one channel and go with that because previous owners have has unbalanced set-ups that wore the two side of the groove very unevenly. It is pretty obvious when this happens because noise and distortion are much worse on the bad side. My first guess about your unequal levels is that your cartridge set-up is improper. Recording another or two mono LPs would confirm that.

The several soundcards I've played with do no internal channel mixing. If you choose mono in the recording program they only record from one soundcard channel. You don't have a choice which one.
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cliveb
post Nov 22 2005, 10:11
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QUOTE (singaiya @ Nov 22 2005, 04:02 AM)
But this led me to wonder: if I had set the program to record in mono in the first place, how would it convert the "stereo" signal it receives from the soundcard?
....
And another related question: have any of you noticed differences in channels with mono vinyl sources? I'm wondering if this is due to poor vinyl pressing, cartridge misalignment, or other.
*

Firstly, I agree with the other posters who have suggested that the channel imbalance is likely due to cartridge misalignment or uneven wear on the record. Genuine mono records are cut with mono cutter heads, which have no vertical component whatsoever, so in principle it is impossible for them to cut the two channels differently. Of course, minor mechanical imperfections could affect this, but it seems very unlikely that there could be big enough errors that they would be audible.

I also wanted to make a comment about your speculation regarding recording the records in mono to start with. Don't do this - always record in stereo, and mix down to mono as a final step. The moment you mix down to mono (whether it be via rewiring the cartridge, summing the signals in the preamp, or at some later stage in the PC), you eliminate a valuable option of choosing the better channel when doing any restoration work. If you're doing a careful manual restoration, choosing left or right will change as you work along the recording. You'd be surprised how many clicks and pops on mono records are present only on one channel - pasting over from the undamaged channel results in a virtually perfect repair. When you make the final mix down to mono in software, you'll still benefit from the ~3dB reduction in background noise.
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Axon
post Nov 22 2005, 18:00
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A lot of people think that just using a mono cart (ie conical tip and mono outputs) gives better results than recording in stereo, even when the noise reduction after the stereo recording is taken into account. Any opinions on this?
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mdmuir
post Nov 22 2005, 18:12
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QUOTE (Axon @ Nov 22 2005, 12:00 PM)
A lot of people think that just using a mono cart (ie conical tip and mono outputs) gives better results than recording in stereo, even when the noise reduction after the stereo recording is taken into account. Any opinions on this?
*


I have used the mono stylus that was offered for the Stanton 881s when recording mono cut l.p.s. The playback was usually cleaner than from a stereo stylus. The particular stylus for that cartridge was rated for 3-5 grams tracking weight, a good deal more than the 1-1.25 grams for the stereo stylus. I am not sure if stanton is still making the mono stylus for that cartridge or not.


--------------------
you will make mp3's for compatibility reasons.
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AndyH-ha
post Nov 22 2005, 18:30
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A mono stylus is a completely separate consideration from a mono cartridge. A mono stylus is a different size and shape, to match the groove characteristics of mono LPs. This can give better results in some cases.

A true mono cartridge, I believe, has no possibility of vertical movement. Recently some of the high end companies have started offering mono cartridges. Possibly those are of this construction. Possibly the benefits of this are similar to those of many other audiophile speciality items.

However, most things that have been offered as mono cartridges for a good many years are stereo cartridges with the two channels wired together for output. This gives the advantage of noise and click reduction through cancellation if you are just playing the records for listening, but I believe getting both channels separately into the computer, where you have much greater control, is a real advantage when doing transfers.
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AndyH-ha
post Nov 22 2005, 18:30
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In some cases it will be advantageous to do other processing before converting to mono, in some it will make little or no difference to the final result, but there are those cases where dong very much processing will significantly reduce the (potentially) large benefit of the conversion process, especially when the LP (or 78) has had the surface badly beaten up by poor handling over the years.

Converting to mono at or near the beginning of processing will often remove a major portion of the clicks and pops, sometimes to an extent that seems almost miraculous. The first benefit, of course, is that you therefore need to put zero effort into the particular defects that are no longer present. Also, depending upon the audio editor you use, it is still as simple to copy small sections from either original channel into your mono track as it would be if you were still working on the two track "stereo" recording (although you would need to first amplify that original by 3dB) .

Large pops and clicks, from large scratches, can have results that extend well beyond the obvious spike. The process I mentioned, where the convert to mono step produces two different track (one the sum -to keep, the other the difference -- to discard) sometimes illustrates this clearly. Other (correct) convert to mono methods will give the same benefits, you just don't have the difference track to illustrate what has been removed.

A large click (effecting both channels) may produce a trailing low frequency wave form (possibly a damped oscillation?) that can extend more than 200 ms beyond the obvious spike. Before separating into these two opposite characteristics tracks, that trailing portion cannot be visually distinguished from the music it is mixed into. Declickng the obvious spike in the "stereo" tracks often leaves much of the rest. That part is sometimes very audible as a thumping sound, yet it can be very difficult to exactly locate and correct. Often, converting to mono at the beginning will completely remove the entire problem to the difference track.

Maybe you can successfully remove that lower frequency remainder by combining the left and right to mono after declicking, but too often your declicking efforts, either auto or manual, differentially effect the two channels. Now they won't combine with such effective canceling results as they would have before you screwed with them. This is also the case when you copy part of one track to the other. In many instances, doing the mono conversion first eliminates most or all of these problems.

I was originally convinced that auto declicking worked best on the original recording, which may be true for a large percentage of moderate clicks. The trade off there is that many of those clicks just won't be there if you convert to mono first. I changed my approach after spending frustrating hours and hours trying to repair the damage of very large clicks in an LP transfer. When I finally went back and did the convert to mono as my first step, a large part of the agony went away without further effort.

Now I keep the sum and difference tracks together as I process through the rest of the steps. The difference track often shows me a large, easily visible, version of what small remainders still exist in the real mono track.

This post has been edited by AndyH-ha: Nov 22 2005, 18:33
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cliveb
post Nov 22 2005, 19:26
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QUOTE (Axon @ Nov 22 2005, 06:00 PM)
A lot of people think that just using a mono cart (ie conical tip and mono outputs) gives better results than recording in stereo, even when the noise reduction after the stereo recording is taken into account. Any opinions on this?
*

Yes, I have an opinion: you shouldn't do it. Always record in stereo, to maximise your chances of finding a clean(er) side to a damaged groove that will be easier to fix. I even record 78s in stereo as an aid to restoration.

If I have understood him correctly, Andy has speculated that automatic declickers can sometimes affect the two channels differently in a way that may screw up the later mix down to mono. That may well be the case, but if you want to do vinyl restoration properly you shouldn't be using automatic declickers if the first place. When declicking a mono record, for each click find the channel that's least damaged, repair it, then copy it over to the other channel. Even if you do let an automatic declicker do its stuff, you can still select the better side and copy it over afterwards to avoid any mixing gremlins.
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singaiya
post Nov 22 2005, 20:13
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Thanks for all the replies. I thought about testing some other mono vinyl (re differences in left & right channels), then I thought that I probably can't conclude much about my setup from it since probably all of my mono records were purchased used (is new mono vinyl made?). So I can't rule out that it wasn't other people's misaligned cartridges that caused some outer groove damage. Besides, I usually buy a decent cartridge at a good stereo store every few years, so I think my stuff is ok. On this record neither channel had any pops, or annoying clicks or crackle. It was just the right channel sounded severely lowpassed.

From now on I'll record to stereo and keep the good channel if there is a drastic difference, e.g. 100% L, 0% R. If no noticeable difference, I'll see if any pops or clicks need removing, then let it auto combine them 50/50.

Thanks again everyone.
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Bill02888
post Nov 22 2005, 21:29
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I've got a small collection of records (78s from the 20s to more recent discs from the 80s) that I'd like to "rip".

What are you folks using for pre-amps for the sound card input? My cartridge (I forget the make/type -- sorry) puts out a fairly low signal so a pre-amp is a definite "must" for me.

Also, how are you applying the various curves (RIAA and pre-RIAA) to the cartridge signals? Hardware? Software? If software, what software?

Thanks very much!
Bill

This post has been edited by Bill02888: Nov 22 2005, 21:30
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singaiya
post Nov 22 2005, 21:38
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Most of us will refer you to CliveB's excellent primer on the subject, which will answer any question you might have:

Transferring LPs to CDR

But the direct answer is to use your stereo amplifier/receiver, assuming you have one, using the tape output. That is, treat the soundcard as if it were a tape deck. Your amp/receiver's phono input has the RIAA adjustments built in.
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Bill02888
post Nov 22 2005, 21:41
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Alas, RIAA is "fairly recent". I'll need to apply different curves to the older 78s. I'll check out that CliveB link!

Thank you!
Bill
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singaiya
post Nov 22 2005, 21:47
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You probably already know this, but the 78s require different cartridges than normal 33/45s in order to be played back normally. Victrola's often had cartridges that could select between 78 & 33/45 needles -- I'm not sure if those kind are available for normal turntables....
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woody_woodward
post Nov 22 2005, 22:58
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QUOTE (Bill02888 @ Nov 22 2005, 12:41 PM)
Alas, RIAA is "fairly recent". I'll need to apply different curves to the older 78s. I'll check out that CliveB link!

Thank you!
Bill
*

Audacity has software equlization. There are predefined curves for RIAA, several pre-RIAA LP's, 78's. There was even one for acoustic recordings. Audacity is, of course, freeware.
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Bill02888
post Nov 23 2005, 04:47
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Audacity! Neat! I'd downloaded it a while ago, but decided to stick with GoldWave (been using GoldWave since ... well, a LONG time ago! When it came on floppy and with a user's guide!). I'll check that out. Thank you very much for the tip!

Bill
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cliveb
post Nov 23 2005, 10:06
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QUOTE (Bill02888 @ Nov 22 2005, 09:41 PM)
Alas, RIAA is "fairly recent". I'll need to apply different curves to the older 78s. I'll check out that CliveB link!
*

You won't find any help with different EQ curves for 78s on my page: it's very much aimed at restoration of vinyl LPs, not 78s. To be honest I don't know a great deal about 78s, although I have restored about a dozen (and discovered that it helped to record them in stereo, as I stated earlier in this thread). Based on my experiences with 78s, I'd say that they have bigger problems than the minor response variations you get if you use the wrong EQ curve. Gross frequency imbalances can be adjusted afterwards in software.
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