Hello. A show or two Dave was ruminating with a caller about his need to stuff long talk files onto CDs. There is one point that I think nobody observed and that is this: Whatever program is saving your data wants to save it in stereo because of course it’s stereo. But talk doesn’t need to be stereo. And going mono halves your file size.
Unless of course it has to be a Red Book CD.
WFMU, the best radio station, doesn’t do anything in stereo and their archives have decades of around-the-clock radio available in adequate radio sound quality.
Going mono only halves the size in uncompressed formats. MPEG for example notices that the signal is the same in both left and right channels and encodes it only once.
You can also reduce the sampling rate and bit depth for speech. For example, the PSTN has a raw rate of 64000 samples per second and 8 bits each, except the μlaw codec makes the samples seem as if they have approx. 12 bit range (if they were done with straight linear PCM). A popular format is 22.5K 16 bits, which is fine for speech. 48 kilobits per second for MP3s is usually plenty for speech.
So is there a standard besides Red Book that supports a double length mono track; one that’s commonly supported by CD players? I’m not counting ones that play compressed formats like MP3. In trying to answer that question I came across an interesting workaround. Split the first and second parts of the recording onto each channel, then listen to each part with the stereo panned left then right 🙂 Apparently some old CDs were actually issued where that was intended.