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ReplayGain query

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DefineByte:
Am I correct in thinking that ReplayGain works in the same way as the software EQ i.e. it's done using the CPU?

Is there a technical reason why Rockbox couldn't use a player's built-in volume adjustment (is that using the DAC? I don't know) in a sort of optional low precision ReplayGain mode (on compatible outputs)?

It would save significant battery life, would it not?

baobab68:
I think it does use the CPU. I had a developer tell me that it's not expensive in terms of CPU usage - it only causes one extra "multiply" for each sample - ie multiply the amplitude by the scaling factor represented by the Replaygain value.

I do see your point though, but I don't have the tech knowledge to comment, sorry.

saratoga:

--- Quote from: DefineByte on August 04, 2007, 04:25:57 PM ---Am I correct in thinking that ReplayGain works in the same way as the software EQ i.e. it's done using the CPU?

--- End quote ---

Thats correct.  


--- Quote from: DefineByte on August 04, 2007, 04:25:57 PM ---Is there a technical reason why Rockbox couldn't use a player's built-in volume adjustment

--- End quote ---

Because replaygain is a digital adjustment, and must be done prior to loading samples onto the DAC.  RG actually takes each sample and multiplies it by a constant.  You can't do that with a DAC.


--- Quote from: DefineByte on August 04, 2007, 04:25:57 PM ---It would save significant battery life, would it not?

--- End quote ---

I don't think replaygain is CPU intensive enough to have a noticeable impact on CPU performance.  Its just 44,100 16 bit multiplies per second.  Thats not very much CPU time.

mamboman:
good to know that. i find that it's very useful so that i don't have tracks jumping from quiet to loud and all over the place

Lear:

--- Quote from: DefineByte on August 04, 2007, 04:25:57 PM ---Is there a technical reason why Rockbox couldn't use a player's built-in volume adjustment (is that using the DAC? I don't know) in a sort of optional low precision ReplayGain mode (on compatible outputs)?

--- End quote ---
For the "Prevent Clipping" option to work, the volume adjustment has to be done before the samples are scaled/clipped to the final output (which happens before the samples are sent to the DAC). And if you don't use the clip prevention, using Replaygain is likely to reduce any clipping introduced by a lossy encoder.

Besides, it's much easier this way. No need to worry about exactly when a certain sample is played. And using the volume adjustment wouldn't work well when using crossfading.

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