Normalize During Ripping Or Encoding?

2002-01-06 20:50:58

Is there a preference.

In my mind, it would make more sense to use EAC's normalizing, since I can tune it to only normalize those tracks that fall into a specific range. If I normalize during encoding, then it would normalize everything wether it need it or not.

Is this correct?

Brett

Normalize During Ripping Or Encoding?

Reply #1 – 2002-01-07 01:34:01

Use mp3gain and normalise AFTER encoding.

http://www.geocities.com/mp3gain

Normalize During Ripping Or Encoding?

Reply #2 – 2002-01-07 04:30:04

I guess I don't understand.

How does it help to change the gain of an MP3 file if the clipping was present in the WAV file before it was even encoded?

I would end up with an MP3 that is still clipped only at a reduced volume.

What am I missing here?

Brett

Normalize During Ripping Or Encoding?

Reply #3 – 2002-01-07 06:29:11

Clipping doesn't occur in the original wave unless the recording was done really poorly. In anycase, that is nothing to can do anything about.

Clipping occurs on DECODING. During encoding, the original wav is transformed to some values and during the reverse transform, the decoded values may fall outside the range of the playback medium (+- 32767 for 16 bits).

Scaling/Normalising the original wav by 95% doesn't remove clipping from the original wav. It just reduces the chance that clipping will occur on playback. Of course, scaling and normalising introduces noise and distortion before the encoding stage. Not a good thing.

Mp3gain is better because it allows you to encode the original wav, then it decodes the wav to check that maximum decoded value to see if clipping occurs. It then calculates how much it needs to attenuate the decoding (in 1.5 dB steps) to prevent clipping from occuring. It then applies this attenuation value as a Global Gain value to the entire MP3. This does not change anything in the MP3 except add information in the headers to tell the player to attenuate the output by this amount when decoding.

This process is therefore as lossless as you can get, giving you the best quality encode, and best playback without clipping. You don't have to guess the amount to attenuate or scale by, this is all calculated automatically. You won't be attentuating unnecessarily when there is no need to, and you won't run into the situations where you don't attentuate enough.

On top of that mp3gain also allows you to do useful things, like increasing the playback volume to use the entire range for low volume samples (e.g. dvd rips). mp3gain also allows you to make your entire collection playback at the same approximate volume.

Normalize During Ripping Or Encoding?

Reply #4 – 2002-01-07 12:43:40

Thanks.

That explained it pretty well. Thanks. I'll give mp3gain a whirl.

The thing that got me looking at this was one of my Metallica CD's. When I looked at the mp3 in Cool Edit, the peaks were completely off the scale.

I then ripped the CD again, and looked at the WAV files in a more professional audio mixer program (Ntrack). During playback it was crossing 0db and clipping.

The CD in question was "Load".

When I normalized it (with EAC) the entire waveform looked like it had been sawed off across the top. Not exactly what I was looking for either.

Brett

Normalize During Ripping Or Encoding?

Reply #5 – 2002-01-07 20:38:09

Hi, all.
Tangent, as you might remember, yesterday I asked a similar question and this thread gives me some more information.
What I learned is that normalising wavs before encoding is definitely a nono !
What I don't understand is the following: if the extracted original wav doesn't clip and I mp3 encode it, then the resulting mp3 file doesn't clip either, because as you said, clipping occurs on Decoding.
But where exactly can the track clip then. What I do is take the mp3 and play it in WinAmp. As far as I understand my PC, when I turn all the volume settings (winamp, soundcard) to maximum (not in the winamp eq), the output to soundcard will be of the exact level the file was encoded with, because all the volume settings can only lessen the volume. So the only clipping that can occur will be produced by the soundcard's (pre)amps or the speakers or headphones... right ?
If this is so, IMO, I can stop all this normalising fuss, because the file itself is absolutely flawless concerning clipping.

Normalize During Ripping Or Encoding?

Reply #6 – 2002-01-07 20:56:59

When Winamp plays your mp3's, it is decoding them in order to play them through your computer's soundcard.  The clipping thus occurs during playback.  The output of the soundcard will be at the exact level of encoding, but because mp3 (and ogg, etc.) is a lossy format, it won't necessarily be exactly the same as the original wav file, and thus the result may be outside of allowable playback range.

Normalize During Ripping Or Encoding?

Reply #7 – 2002-01-07 20:57:07

See:

http://ff123.net/clipping.html

Also:

http://ff123.net/norm.html

ff123

Normalize During Ripping Or Encoding?

Reply #8 – 2002-01-07 21:28:48

Will the adjustments made by mp3gain also work on hardware playback, or is this metadata that only software players like Winamp will recognize?

Brett

Normalize During Ripping Or Encoding?

Reply #9 – 2002-01-07 21:40:58

So, here I am again. I read the articles ff123 linked to (thanx for this huge amount of info).
What I learned again is:
- Worst is to let eac or cdex do the normalizing before encoding
- better to let lame do it (scale, right?) while encoding
- best to let the player do it, provided that the information to do so is in the file

mp3gain is such a method, but it's not supported by any players yet, right ?

mp3 compression is lossy; but the amount of information one could lose when letting the encoder do the job is - compared to the amount of information in the file - almost not existant.

my last question on this: do the alt-preset standard and fast standard settings in lame do scaling ?
if yes, I'll be alright with this.....

Normalize During Ripping Or Encoding?

Reply #10 – 2002-01-08 05:47:14

Clipping occurs when a sample is decoded to be outside the 16bit range (-32768 to 32767). That sample value will be 'clipped' to -32768 or 32767 when decoded. During playback you will hear the clipping artifacts. Usually it's not audible unless more than a certain number of continous samples are clipped.

Normalize During Ripping Or Encoding?

Reply #11 – 2002-01-08 05:50:01

Global Gain (used by mp3gain) should be supported by all compliant MP3 players.

Normalize During Ripping Or Encoding?

Reply #12 – 2002-01-08 13:05:49

OK, I'm convinced. I'll do it with the mp3gain proggie.

But -what else can it be- I have a few questions on this, too.

The Glen Sawyer proggie applies the chosen volume level to the complete file. If one likes, he can do this on a per album basis so that the complete album is one volume level.
Wouldn't it be better to apply a volume level adjustment only to frames where clipping COULD occur instead of ALL the frames ? I ask this because I think that also mp3gain leads to a falsification of the content of the encoded signal, right ? Because after 'mp3gaining', noone will know what the original global gain value was. Then why not minimize the change to a few frames ?