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Subject: Re: Sound quality with Rockbox
From: Linus Nielsen Feltzing (linus_at_haxx.se)
Date: 2002-12-09


George Styles wrote:
> i also have the subjective idea that the Archos sounds slightly better, but
> I have not experimented with the various settings etc. it may be something
> as simple as the default loudness setting...

I think so too. There is little we can do about it. Still, I can add
some new interesting settings for the Super Bass that are hard coded at
the moment. For all tweakers out there.

> what do u mean by digital distortion? do you mean a buffer overload, or are
> you scaling the MP3 data somehow so its clipping?

We don't do anything to the MP3 data, we just pass it to the MAS DSP.

The MAS DSP processes the audio according to our settings (Bass, Treble,
Loudness, Volume) without any compensation for overflow in the calculations.

This means that we must make sure that the sum of the settings do not
exceed 0dB. If we set Bass/Treble to 6dB, we must set the volume to -6dB
to prevent overflow. We do not do that today, mostly because of
lazyness, but also because we want to allow people to use the settings
they want. You *can* set Bass to +12dB and still get no clipping, either
because the volume is low enough, or that the mp3 audio has a generally
low level so clipping does not occur.

If we add a compensation algorithm, people will not be able to listen to
low level audio.

I still intend to add compensation, but only as an option for those who
need to set the bass/treble/loudness high and don't want to adjust the
volume themselves.

/Linus



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