Two different mono channels in 1 track

[steve]

I have read that playback of single channel through both speakers typically works, but may not--depending on the sound card. Is that not true? Or will it invariably work, regardless of sound card, hardware, connections to a home stereo, etc?

Playing back a mono track should always play back through both speakers (assuming no faulty hardware).
The reverse is not true though. When it comes to recording a mono (one channel) input onto a 2 channel track, some sound cards will map the mono input to both channels, but other sound cards will send the input to only one channel, giving silence on the other channel. Most high quality sound cards produce the latter behaviour.

Can you expound on the bit about "higher quality if exported at the same bit rate than the 2 channel version"? I can understand how a single channel version would save space, but the "higher quality" thing throws me a bit. I'm guessing you'll say something about all the bits in a single channel means more info in that single channel, therefore higher fidelity?

Yes that's exactly what I'll say. All the bits in a single channel means more info in that single channel, therefore higher fidelity.
There are a couple of issues here though.
<<if exported as an MP3 file it will be higher quality if exported at the same bit rate than the 2 channel version.>>

Using Audacity, if you export a file at 128 kbps CBR (Constant Bit Rate), then the file will be exported with 128 kbits for each 1 second of audio, regardless of whether the file is mono or stereo. So exporting as mono will provide 128 kbits for each second of that one channel, but exporting as stereo will only allow 64 kbits per channel.
If you do export as 128 kbps stereo (2 identical channels), then using the "joint stereo" option will provide quality benefits over the "stereo" option, but it will still work out as a lot less than 128 kbps per channel.

Running a test:
128 kbps CBR 2 channel mono encoded with the "stereo" option sounded BAD.
128 kbps CBR 2 channel mono encoded with "joint stereo" sounded OK'ish
128 kbps CBR 1 channel mono sounded good.

If you export as VBR (Variable Bit Rate), then the situation is different. The VBR settings target a specified "sound quality" rather than a specified "bit rate". VBR encoding will change bit rate dynamically according to the complexity of the sound. Because a mono (1 channel) track is "less complex" than a 2 channel track, VBR encoding will reduce the bit rate when exporting a mono (1 channel) track, so the file size for a 1 channel track will be less than the size of a 2 channel track and the bit rate per channel will be much closer.
For example, using VBR Quality 5 on a test sample:
Source . . . . . . . . . . . . Actual Bit Rate
1 channel mono . . . . . . . 78.4 kbps
2 channel mono . . . . . . . 103 kbps (joined stereo)
2 channel mono . . . . . . . 146 kbps (stereo)
2 channel true stereo . . . . 155 kbps
(the test sample was Koz's "classic" piano sample (16 bit 44.1kHz stereo WAV).
Just to confuse the issue - just because the VBR settings aim to produce a specified sound quality does not mean that exactly the same sound quality is achieved in each case.
The 2 channel mono track when encoded as VBR stereo produced a marked difference between the left and right channels making it sound "less mono". Subjectively the VBR stereo may be preferable as it sounds more "spacious", though it is obviously due to inaccuracies and not true stereo. The differences between left and right channels when using VBR joint stereo was much less marked.
The sound quality for each of the mono VBR tracks was extremely similar, though I thought the true mono track (78.4 kbps) sounded marginally better than those encoded from the 2 channel mono tracks.

As might be expected, 128 kbps CBR mono sounded the best (equivalent to 256 kbps for a stereo track), closely followed by the VBR encoded files. The 2 channel 128 kbps joint stereo CBR was noticeably less good, and with the "stereo" option it sounded terrible.
As a comparison, I also encoded the 1 channel mono track as VBR Q1 and Q0. These produced actual bit rates of 125 kbps and 134 kbps (so a similar file size to the 128 kbps CBR) and sounded excellent.

Conclusion - for mono audio, VBR Quality 1 or 0 encoded from a 1 channel track provide excellent quality in a small file size.
Don't use the stereo option with CBR encoding for 2 channel mono audio at medium or low bit depths.

[steve]

I have seen some barebones editors that can supposedly do a basic edit of an mp3 (cutting a segment, doing a fade) without recompression--allegedly, I say allegedly.

MP3Split can do basic (cut and trim) editing on MP3 and Ogg files without decoding/re-encoding. http://mp3splt.sourceforge.net/mp3splt_page/home.php

[ignatz]

Thanks for the fine points. I have saved all of that to a Word file for later study. I may actually run some tests of my own.

My default mp3 export choice for music files is VBR, quality 2, joint stereo--regardless of whether the 2 channels are "stereo" or identical or whatever. In reality, they are virtually identical ("mono") more often than not.

I'll likely stick with that. Space is not an issue. Converting 2 track mono to single track mono would save space, but would involve compression and might cause audible degradation, not to mention being extremely time consuming.

Everything I have read says that VBR and joint stereo have few drawbacks for mp3, so I'll ride with that until I read otherwise.

[ignatz]

I have seen some barebones editors that can supposedly do a basic edit of an mp3 (cutting a segment, doing a fade) without recompression--allegedly, I say allegedly.

MP3Split can do basic (cut and trim) editing on MP3 and Ogg files without decoding/re-encoding. http://mp3splt.sourceforge.net/mp3splt_page/home.php

I think mp3 Direct Cut is another such app.

http://mpesch3.de1.cc/

There is also mp3Trim/Wavtrim, which says they don't decode-reencode:

http://www.mptrim.com/

I have used Direct Cut, but not Trim.

[rorser]

First make darn sure you have a good file of your original work. I would probably export as WAV in addition to the Project.

Then you can use the tools under the little black arrow on the left.

Split Stereo Track > Delete one track. Edit > Duplicate > Make Stereo Track. Export as WAV or save a new, different Project.

Open the original Project and go through that whole thing for the other track.

That's the short version. Let me know if you can't find some of the tools.

Koz

Koz, simple,easily understood instructions. It seems important how one deletes the unwanted channel. How do you suggest? First time I just closed the channel I was not using, using the X for the track--at left of the screen. Then after I duplicated the channel I was working with, the playback was of only one channel. But, selecting and deleting followed by duplication seemed to work.

[rorser]

I did some experimenting and this seems to work. There may be a more elegant method.

Split stereo track from the black arrow/triangle

Put cursor in top channel

Edit, move cursor to track start (cursor is now at beginning of top channel)

Edit, select cursor to track end (top channel is now highlighted)

Edit, copy (top channel is now on clipboard)

Put cursor in bottom channel

Edit, move cursor to track end (cursor is now at end of bottom channel)

Edit, paste (top channel now has been appended to end of bottom channel)

Edit, move cursor to track start (cursor is now at beginning of bottom channel)

Edit, select cursor to track end (entire bottom channel containing both original channels is now selected)

Edit, copy (entire bottom channel containing both original channels is now on clipboard)

Put cursor in top channel

Edit, move cursor to track start (cursor is now at beginning of top track)

Edit, select all (entire top channel is now highlighted)

Edit, paste (top channel overwritten with contents of clipboard; both top and bottom now have same content)

Make stereo track from the black triangle/arrow

Export

I tried a couple of other variations that will probably play back on both L and R channels, but these other variations showed as a single channel when reopened in Audacity. The method outlined above opens as two channel.

This sounds like a fool-proof way to do this. Thank you. I have a bunch of reels that need this treatment.

[rorser]

I have seen some barebones editors that can supposedly do a basic edit of an mp3 (cutting a segment, doing a fade) without recompression--allegedly, I say allegedly.

MP3Split can do basic (cut and trim) editing on MP3 and Ogg files without decoding/re-encoding. http://mp3splt.sourceforge.net/mp3splt_page/home.php

I think mp3 Direct Cut is another such app.

http://mpesch3.de1.cc/

There is also mp3Trim/Wavtrim, which says they don't decode-reencode:

http://www.mptrim.com/

I have used Direct Cut, but not Trim.

I am assuming that all this preceding mono/stereo quality discussion does not affect me if I do as you say and copy and paste the mono left channel to the right channel (using either Koz's or Ignatz's method) and then save the aup. project and eventually to .flac . Is that correct guys?
Gratefully, Richard

[steve]

I am assuming that all this preceding mono/stereo quality discussion does not affect me if I do as you say and copy and paste the mono left channel to the right channel (using either Koz's or Ignatz's method) and then save the aup. project and eventually to .flac . Is that correct guys?

That's correct. We seem to have gone wondering off down the garden path after your original question was answered.
If you're sticking with lossless formats (WAV and Flac) then the discussion that followed (from ignatz's enquiry re. MP3's) can be ignored.

[rorser]

>>If you're sticking with lossless formats (WAV and Flac) then the discussion that followed (from ignatz's enquiry re. MP3's) can be ignored.<<

Thank you Steve (& Ignatz & Koz) for all your help. It has made my project so much more pleasant having the support of all you guys.