Question about post-gain..

[MoonWalker]

What exaclty is post gain? I didn't found any information on the forum..Is it a DSF that does what auto-gain does??

MoonWalker

[DSPguru]

pregain is the regular gain everybody knows - change the volume of the signal before processing it (eg, encoding to mp3).
postgain is a method were gain is being asserted after processing the signal (eg, encode to mp3 and find the maximal gain at the same time, then raise up the volume by modyfing the global_gain).

Postgain information needed to be supported by players.
mp3, ac3, aac postgains are supported by all players, ogg postgain isn't.

as far divx encoders care, support for ogg postgain by the ogg dsf is all that needed, and should be introduced soon.

[MoonWalker]

Thanks very much DSPguru for your quick reply..

MoonWalker

[JimmyBarnes]

Originally posted by DSPguru
pregain is the regular gain everybody knows - change the volume of the signal before processing it (eg, encoding to mp3).
postgain is a method were gain is being asserted after processing the signal (eg, encode to mp3 and find the maximal gain at the same time, then raise up the volume by modyfing the global_gain).

In BeSweet (GUI), if I check Auto Gain only, it does a scan to find the maximum gain allowable before processing the original soundfile. However if I check both Auto Gain and Post Gain, it starts processing immediately. Does that mean the max gain determination is skipped?

thanx
JB

[raistlin2k]

NO, but normal auto-gain gets set on every frame when it gets transcoded from input to output; post-gain gets set at the end of transcoding, in the tag of the file. so a pre-scan is not necessary, gain gets evaluated on transcoding. the need of a tag for post-gain explains why it cannot be used on wave-files, but only on mp3 ,aac & ogg.

Hope you see it clear now
Raist

[JimmyBarnes]

Originally posted by raistlin2k
NO, but normal auto-gain gets set on every frame when it gets transcoded from input to output; post-gain gets set at the end of transcoding, in the tag of the file. so a pre-scan is not necessary, gain gets evaluated on transcoding.

Still can't see how it finds the global max gain required for the whole soundtrack without doing a pre-scan

JB
:confused:

[DSPguru]

Originally posted by DSPguru
postgain is a method were gain is being asserted after processing the signal (eg, encode to mp3 and find the maximal gain at the same time, then raise up the volume by modyfing the global_gain).