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Topic: -a vs -mm? (Read 3498 times) previous topic - next topic
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-a vs -mm?

OK, I'm stumped - what's the difference between the -a switch and the -mm switch?
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

-a vs -mm?

Reply #1 –
Not much difference...

-a    downmix 
Mix the stereo input file to mono and encode as mono.
The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.

This option is only needed in the case of raw PCM stereo input (because LAME cannot determine the number of channels in the input file).
To encode a stereo PCM input file as mono, use "lame -m s -a".

For WAV and AIFF input files, using "-m m" will always produce a mono .mp3 file from both mono and stereo input.


-mm  stereo mode
mono
The input will be encoded as a mono signal. If it was a stereo signal, it will be downsampled to mono. The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.
Juha Laaksonheimo

-a vs -mm?

Reply #2 –
I understand everything except the bit about using "lame -m s -a" - wouldn't that downmix the file to mono, but then encode it as a stereo mp3?
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

-a vs -mm?

Reply #3 –
No, -m s -a will downmix to mono and encode it as mono.

You can check this yourself with CoolEdit or something...
Juha Laaksonheimo

-a vs -mm?

Reply #4 –
Well, then, I'm confused - according to lame --help, -m s gives you (s)tereo mode...
It's is not, it isn't ain't, and it's it's, not its, if you mean it is.  If you don't, it's its.

-a vs -mm?

Reply #5 –
I guess the answer is that if you are going to downmix to mono you want 2 discrete channels to start with and not joint stereo which would confuse the issue. (Sounds reasonable, but I am only guessing!!)

john33