( Pretty good memory there! Glutamoto was a take-off on Godzilla from the Firesign Theatre's 1972 album NOT INSANE. I had to use an alternate (glutamo
do) spelling since the correct one was already taken on AOL. )
I don't think you're going to be able to get any more PCM minutes onto an audio CD. You can cram a lot more mono MP3 files onto a data CD though!
My making mono MP3s dates back to those thrilling days of yesteryear when saving bandwidth and file size was much more important. I found that, as you noticed, if you don't need it in stereo, you can save a lot of file size if you go mono. Back then it was an option on the program I used at the time to make MP3s. Nowadays I use CDEX. And it's got tons of different settings on it. I usually go with an ABR/VBR setup. When you go mono you can drop your bitrate settings in half and still get the same fidelity.
I'm not sure how the computer determines the average bitrate - you can find that just by hovering over the file name in Windows, file explorer. I actually had the bit rate set up on this particular MP3 to average 80kbps with extremes of 64 and 112. It must detect the maximum bitrate on that one. Stereo ones, I've seen it where it comes up with more accurate average bitrates though.
It had been a long time since I made a mono MP3 until the other day. I forgot about the halving the bitrates and just clicked the mono button, and ended up with an MP3 that was nearly identical in size to the stereo one I had just made. Then I remembered and set it up something like this:
MONO:
vs the STEREO setup I think I used:
Here's how the two files compared in size:
There are just so many protocols and parameters you can select when encoding MP3s. I've not done any research on the subject in a few years though. Back then, there was no consensus as to which one was the best. So I took a certain track and made tons of MP3s out of it with different settings comparing sound quality vs file size. I didn't find a whole lot of difference actually, as long as you kept the bitrate up. Usually over 144kbs in stereo I found eliminated most of that "treble warble" you get from compression. 128 isn't bad either, but you can tell it's an MP3 more easily. So I tend to just go with a an average bitrate of 144 or 160, sometimes 128 if the track is not as important, with upper and lower variable points a few notches up and down the scale from the average, and it works. Mono, cut those all in half. (hell, when I buy MP3s online, they come usually in 'insane' 320kbps format, which I transfer to wav then re-encode to the 144 or 160 level)
Then there's the 44khz vs 22khz - I used to make Mp3s in 22khz and get a little bit of savings in file size too, works good if your source is not high fidelity. But it's been so long since I did that, that I can't remember exactly how I did it. I'm sure I had to have them saved as 22khz wav files first. It was certainly before I started using CDEX. I used to "EC's MPEG Suite" before that. I don't have it on my computer anymore, but I do have it on backup CDRs somewhere I'm sure.
Oh, I remember my mom talking about how one of stations back in Illiniois did early stereo broadcasts, AM for one channel and FM for the other. Must have sounded odd with the channels having different fidelity.
-Andy