Anthony Airon Oetzmann airon@gmx.net wrote:

A fairly serious quality question here. I'd like the encoder to scale back the volume of the output before it gets decoded. The reason is that too many encoded files clip when decoded.

I'm assuming you mean you'd like the *decoder* to scale back the volume? As soon as you have an MP3 file the encoder is out of the picture.

I'd like to suggest a way to do this without mucking about in the actual decoding code. It's the way the Waves Renaissance EQ handles it. It actualy calculates with a headroom and at a higher bitresolution. It is able to accuratly tell me how many dB I'm overshooting my output.

MAD already does something similar. Output samples are actually calculated internally with 29 bits of precision, with 3 extra bits of "headroom" for decoded samples that exceed full scale.

What I'd like the MAD plugin to do is have a control setting that tells it to pull x dB out of the final signal, before it gets CUT OFF at the 0dB Full Scale, and sent to the output plugin. I'd suggest a default setting of -2 dB. Perhaps even a clip indicator, if this is possible to display in some way in the Winamp window or another window(on/off switch in prefs).

This might be possible. Scaling the output is easy to do, and wouldn't lose any quality because the internal samples are 32-bit values. A clip indicator might also be easy to add. The trick will be for the user to find an appropriate setting.

Some of you may not hear this revolting distortion. Well I do, and it don't sound good folks. Some songs are mastered to already CLIP on the CD, though they keep that clipped signal below 0dB, as not to make the CD production plant mad(no more than 5 clipping samples on an entire CD is a RED BOOK standard provision where clipped -> 0dB I guess).

Do you hear clipping even with MAD? I ask because MAD doesn't clip the same way other decoders do.

The problem with almost any damn plugin out there is that the volume in fact can only be changed AFTER decoding. Calculating perhaps with 24 + 2 bits would perhaps be advisable, buy I'll leave that to you guys.

I think what you mean is that the volume can typically only be changed after samples have been clipped and scaled to the output resolution (e.g. 16 bits); "decoding" in my mind doesn't include this step. The output of decoding in MAD is 32-bit samples that can be further manipulated without loss of quality before clipping, scaling, and dithering to the output resolution.

If there is consensus among other MAD users, I will consider adding something like this to monitor the amount of clipping and perhaps allow the user to attenuate the signal before output samples are produced.

What do people think?