Joint stereo ?

[Thunderchild]

OK I know what mono and stereo are but what is joint stereo. I find it in mp3 converting programs. does it allow me to keep the file stereo without making it double the mono version ?

[tomd]

Joint stereo can generally be one of two methods:

1. An alternative name for M/S stereo, (Mid/Side), or Matrix Stereo, combining two channels, one of which is the combined mono signal, and the other of which is the difference between left and right.

So M = L + R, and S = L - R.

This way both left and right can be recreated by either M + S (gives left signal) or M - S (gives left signal).

M/S Stereo is often used in professional audio, specifically broadcasting, as it provides a ready mono signal to cope with mono devices.

2. 'Intensity stereo', which is where the parts of the signal that a human would be unable to localise, (ie. it doesn't matter where they are in the stereo field), ie Bass, are recorded in mono to save file size. This isn't used in professional application, only to reduce file size in 'lossy' audio codecs. It's mostly likely this is the term 'Joint Stereo' is referring to.

[ermadea]

Applause, Applause, Applause, Top marks tomd, somebody who knows what they are talking about.(Professional musician?)

[tomd]

Close, but no cigarillo - Sound Engineer.

[Thunderchild]

thanks so what file size can I expect. would this be like 1.5 X mono size ? a good compromize ?

[Space]

the file size doesn't change ( you specify it by choosing a bitrate )

but the sound quality should be slightly higher when you select "joint stereo" ( although I personally can't detect a difference at 192kbps )

[tomd]

No, you've got that wrong - the filesize will be lower at the expense of quality.

It's not a standard process, and as it's applied dynamically it'd not be the same factor of reduction every time. All I can suggest is converting a few copies as a test batch, and see how much they reduce file size.

[Thunderchild]

ok so joint stereo will save some space/allow slightly more quality

[tomd]

No, it doesn't allow more quality - I assure you, Space is totally wrong on that. It's another method of compression, it will reduce file size, but reduce the quality as well.

[Thunderchild]

ok bassically a no no i just go stereo or mono if I want to save space

[tomd]

If it works properly you shouldn't be able to hear the difference between Stereo and Joint Stereo. I'd just rip them in Stereo, mp3s don't take up that much space.

[Thunderchild]

yep my issue was reducing size for e-mail attachments but I just go mono when space is a problem