Mp3 Clipping (caused by encoder) and Apple's Soundcheck

[kurt880]

Hey everyone,

There are a bunch of threads about how loud masters, when converted, to mp3, can have additional clipping introduced by encoding into mp3.

are all (loud) mp3 albums clipped?
Mp3 conversion causes clipping?

If a loud master was to be converted to mp3 in which the encoding process added clipping, would that additional clipping still be present after Apple's Soundcheck is enabled? So for example, lets say that encoding to an mp3 made peak values 2db higher than the source but soundcheck is reducing the volume by 10db, would that extra clipping still be present during playback?

Thanks!

[Greg Reierson]

Unfortunately yes. Once it's in the source, it's there for good.

GR

[kurt880]

Forgive my lack of knowledge on mp3 encoding, but since the audio data is stored in frames containing the volume of each frame, would the clipping still be reproduced? Or is the additional clipping what is actually stored in each frame?

[Th3_uN1Qu3]

No, the way MP3 stores data has nothing to do with the clipping. The clipping is caused by overshoot produced by the steep lowpass filters MP3, and other lossy codecs, employs as part of their data reduction algorithms. The more highs the original recording has, the more overshoot the MP3 will have.

[sonicdefault]

Here's a handy chart I recently uploaded from a Thomas Lund lecture. You might want to watch the videos which cover the loudness war topic on the TC website Here


-SD

[Alexey Lukin]

Originally Posted by Th3_uN1Qu3

The clipping is caused by overshoot produced by the steep lowpass filters MP3, and other lossy codecs, employs as part of their data reduction algorithms. The more highs the original recording has, the more overshoot the MP3 will have.

Lowpass filtering is a contributing factor, but not the biggest source of overshoots. Mp3 introduces overshoots even for a low-frequency material just because mp3 is lossy! Like every approximation of the signal, it has the ability to increase or decrease the level of every cycle of the waveform.

[kurt880]

That's too bad that the extra clipping is there for good. I'd really recommend people check out sonicdefault's video series link, very interesting!

[huejahfink]

I thought that clipping only actually occurs on decoding to fixed point.
If you decode to a 32bit float then all the overshoots are correctly accounted for and a gain change can be made to keep all the info in a subsequent fixed point file.

[Alexey Lukin]

That's right. But since most decoders are fixed-point, clipping is often associated (by many people) with the process of encoding.

[DanDan]

Thanks for the chart SD.
I Master for Download at -2dB FS

DD

[sonicdefault]

Originally Posted by DanDan

Thanks for the chart SD.
I Master for Download at -2dB FS

DD

You're welcome!

I'd love to make it out to Ireland one day, by the way... Such a beautiful place

-SD

[reflection]

If you have clipping mp3s, you can actually UNDO the clipping after the fact.
with the program MP3GAIN

the reason why this is possible is that there is a scale-factor that can be changed in the data of the mp3. this process is lossless, no re-encoding necessary.

the program itself is designed to set an average volume (via replaygain algo) for all mp3s, but you can edit the volume manually in 1.5dB steps, too.
it also analyzes if the mp3 will clip.

very handy if you bought mp3s that clip on most players. (almost all of them do)

MP3Gain - Hydrogenaudio Knowledgebase

MP3Gain - Wikipedia, the free encyclopedia

[DanDan]

Thanks reflection, there's hope!

I'd love to make it out to Ireland one day, by the way... Such a beautiful place

Parts are. The empty centres of the towns and cities and whole ghost estates of empty house ain't though. Nearly a thousand people left every week last year.

So do come, all of you, plenty of room!

DD

[sonicdefault]

Originally Posted by DanDan

Parts are. The empty centres of the towns and cities and whole ghost estates of empty house ain't though. Nearly a thousand people left every week last year.

So do come, all of you, plenty of room!

DD

Wow, I didn't realize that. Was it for economic reasons? I try to keep up with what's going on in the world, but these days, it seems things are tough everywhere.


-SD

[DanDan]

Ireland is rich in many ways, but most of the wealth has and is being stolen.
It was 90% Oak Forest. Gone, which built the British Navy, which built the British Empire. Now the children are being stolen.

A decade of false wealth occurred, based on ridiculously cheap credit courtesy of German savings. The corrupt Government poured petrol on the fire.
My house bought in 95 for 100K, become worth 400K. It is not back down to 200K.

This was our first encounter with wealth. Kids in a sweet shop.

Don't get me wrong. It's still great fun here. Great music everywhere.
We'll be back for another look at the wealth thing. It will probably not be money though. Good quality food and software code more likely.

DD

[Cheebs Goat]

These threads always puzzle me. Who cares if an mp3 clips a bit? Fix the clipping, and you're still just left with an mp3, so it's not like your sonic troubles are over. It's still mangled, and it's probably being played on really bad speakers or buds.