What joint stereo bitrate is equivalent to 64k mono?

Question

I record a podcast, which has so far consisted of four people around a single microphone. After editing, I export at 64kbps mono. This week we're planning to record with two microphones on the table and I plan to export a stereo file, but I'm not sure what bitrate to use to get the same level of quality.

If I were using "simple" stereo, I would have to export at 128kbps (64kbps on each side) in order to get the same quality. However, I understand that it may be a good idea to use Joint Stereo, since the two microphones are likely to pick up a lot of the same sound with only minor differences between them. This would mean that I could achieve the quality of 64k on each side without having to go as high as 128k, right? Would 96k be enough? Would 80k?

Is there a "rule of thumb" or a tool that could tell me what bitrate would be required for joint stereo to achieve the same quality as 64k mono?

Answer 1

Joint stereo is only really useful for actual stereo recordings. What you are recording here (with two microphones on a table) is actually dual-mono, which is very different to "stereo" as there is no correlation between the two channels.

Joint-stereo is only really useful to the encoder when there is correlation between the two channels of the stereo signal. It actually uses M/S and then encodes the "side" signal in such a way that it allows additional bitrate reduction.