How to convert a mono file into stereo

[Quantum88]

All my podcast recordings have always been in stereo and they always will, which is what I want. Unfortunately, Zoom has recently changed this without notice ( one of the many reasons I'm switching to another remote recording platform), and my two recent guest interviews were recorded in mono - which I only discovered when started editing in my Audition today.

I believe that it is possible to convert a mono file to stereo in Audition, but the instructions I saw online talk about blocking and unblocking the "empty channel" - and the problem is that I don't have an empty channel in the audio waveform- there is just one channel.  However the sound comes through both the Left and Right channel in my headphones.

I need to have my podcast in stereo, as it includes some clips that are in stereo (and need to be in stereo) - like music, and my standard intro and outro I simply add to each episode project.

So now I've got two guest interviews recorded in mono which I need to convert to stereo, so that the whole project can be saved in stereo.

How can I do that?  I would be grateful for advice with steps, including enabling two channels in the waveform view.  I work in Windows 10 on a desktop PC, with the current version of Audition (updated yesterday).

[SteveG_AudioMasters_]

It is actually very straightforward, and there's a preset for it too, but you need to alter one thing about it:

With your mono file open, go to Edit>Convert Sample Type. In the presets box select Convert to Stereo. By default it sets the channel levels at 50%, and that's the thing I'd change - to keep the overall playback levels the same (which means that each channel needs to be -3dB down on the mono signal), then change the values to 71%. Then click Okay and it will do the whole thing for you - no need to go through the whole manual process. When you've done this, do a Save As and keep this new file separately, so that you still have the original to go back to if you need it - hopefully you won't.

Now personally I wouldn't do any of this - I'd just assemble the project in a stereo Multitrack session, where you can add mono tracks (with your original file in) and pan them into the mix without any need for converting anything. Much simpler and far more flexible...

[Quantum88]

ok many thanks!

I have just tested it and yes, it saves the whole project to a stereo mixdown file.

I just never even paid attention to it as all my original clips were always in stereo - until now.

thanks again!

[Quantum88]

THANKS so much Steve for this precious tip - I really don't like working with mono files in my editor (they are just strange and different to work with), ALWAYS work with stereo even if they are just speech, so have actually converted each track to stereo - and finally I can breathe! 🙂 

I did change the values to 71% as per your advice, but don't quite understand why this is necessary.

I need to increase the volume which is fine - but is this just the volume or something else?

A quick additional question:  I edit my clips always in the waveformat view (for many reasons it is much easier and quicker for me).  I noticed that the volume of the same clip in the multitrack is about -4 dB or more down on it in the waveform.  Why is that?  I need to increase the volume in the multitrack before mixing.

[SteveG_AudioMasters_]

Fundamentally it's all the same reason. If you have a single mono file and play it back, it will be at whatever level you've set it to. But if you place that file in two channels without altering the level, the playback will appear to be louder - by a few dB, depending slightly on the environment you are listening to it in. To compensate for this, you lower the level in each channel, usually by 3dB.

The level that a multitrack mix produces is dependent on what panning law was in use when you created the session - this is set in Preferences>Multitrack. If you leave it set at -3dB Center, it's effectively doing what I described above - if you pan a mono signal completely to one side, you have to increase it by 3dB to hear it at the same level. If it's panned to the center then it's effectively being created by two channels and you use the law of dB addition to compensate. I'm not going to explain that - it involves some math and people generally freak out if I explain it, so you'll just have to take my word for it (or explore the forum, where you'll probably find an explanation if you look hard enough). The alternative method of panning just reduces the level on one channel to achieve the pan, but it's not really ideal.

The upshot of the pan law issue, though, is that any channel in your mix appears to drop by 3dB in the Master channel when you play it in multitrack. But that's not really an issue, as you can compensate for that either by increasing the master level by 3dB (as you mentioned) or simply normalising your resultant file to whatever level you need the peaks to be at - the end result is the same and because it's a 32-bit FP mix it's lossless.

People make a lot of fuss about this when there's really no need at all, and in fact you can't really set an absolute final level in a multitrack mix anyway unless you are really careful; it's much better to normalize the file to the peak level you want after it's mixed down anyway; that will be accurate; Audition will do that for you much more accurately than you can do it by inspection!

[Quantum88]

Thanks for that.

I don't use pan in my current productions, so both the audio and volume are exactly the same in the R and L channels.  I just like working with stereo files,

I"m still curious why the clip in the waveform (which is also in stereo) is louder by few dB than in the multitrack. Or the clip in the multitrack is few dB lower than in the waveform.  What is causing this?

In my editing workflow I toggle between those two views all the time as I progress editing on the track.  This noticeable difference in the volume is not helpful and I usually need to compensate by raising the volume in the multitrack.

[SteveG_AudioMasters_]

Just set the Master fader to +3dB and leave it there - then there won't be a difference in level. Alternatively, when you do the original conversion to stereo, leave the levels at 100% - that will make the output level what you want it to be (but not actually correct...). The whole process is about accurate level conversions and what you have to do to achieve these.

But as I said, none of it's an issue - just get it sounding balanced and then normalize it afterwards.

[Quantum88]

thanks.

I have just identified another unexplained curiosity with matching loudness - will post it as a separate topic.