Why is there such a variation in sound file sizes?

[BarryH]

I notice that whenever people post their sound files on the site, there is often a great variation in the size of the files. Some under 2mb, others over 10mb.

I just wondered why there was such a variation, what makes a sound file for the same track bigger from some posters than other?

Cheers
Barry

[shadfan4]

I would think 10mb for an Mp3 would be a very large file indeed for a song/tune of 2/4 mins.

I have seen many variations of the bit rate being used for uploaded files. The default size for most mp3's is 128 kbit. (Layer 3 giving approx 10:1-12:1 compression) Better quality is achieved with 192kb but once you get past 320 kb the quality is hard to detect for most peoples ears and it increases the file size dramatically.

I have not seen many posts that are .wav files, as these for most, could take all day to download unless you have a nice fast broadband connection.

As I mentioned a .wav file would be approx 10-12 times larger than Mp3 128 kb.

Cheers

Mike

[martyn]

I'd be interested to know, when a .wav file's compressed to an mp3 one, what exactly's lost in the process.
I've played .wav files I've recorded and then played the converted-to-mp3 ones to compare and aside from a minimal 'something' loss I can't really say which I prefer or why. When I say 'something', the mp3 files do seem to have lost a bit of the roundness or smoothness of the original - can't be more specific, but given an mp3 file's around three to four mb, whereas my original .wav file can be up to 57mb, something's obviously disappeared somewhere in the transition.
Any explanations without mind numbing techno-speak would be appreciated - have huge problems trying to understand such matters without the eyes glazing over, accompanied by random thumb sucking . . . could be my age, of course . . .

[graeme]

Sept 10, 2009 16:53:21 GMT martyn said:

I'd be interested to know, when a .wav file's compressed to an mp3 one, what exactly's lost in the process.
......Any explanations without mind numbing techno-speak would be appreciated. . .

Well, it's a bit difficult to explain how all this stuff works without some techno-speak, since it's a highly technical subject. One of the simplest explanations I found is this one:

"Definition of: perceptual audio coding

A technique for further compressing digital sound by eliminating frequencies that cannot be perceived by the human ear. Frequencies that are too low or too high are eliminated as well as soft sounds that are drowned out by loud sounds. When several musical instruments are playing simultaneously, depending on frequency and volume at any given moment, the sounds from one instrument can cancel out the sounds of another. The frequencies that cannot be heard are removed.

Perceptual audio coding uses the psycho-acoustic algorithms developed by Dr. Amar Bose, inventor of the Bose speakers and whose company is known for its quality audio products. MP3 uses perceptual audio coding to dramatically reduce the amount of digital data on a music CD."

[didier]

Sept 10, 2009 16:53:21 GMT martyn said:

I'd be interested to know, when a .wav file's compressed to an mp3 one, what exactly's lost in the process.

There is always some loss with mp3 (the same with wma and AAC), but not all codecs are equals. You'll get better results with Lame or MP3 Pro than with the standard MP3 codec.

With the best codecs, the loss at 128 kbps is not much noticeable, unless if you use high-end playback equipment.

The are lossless digital compression systems, such as the MLP (Meridian Lossless Packing), but it only provides 2:1 compression, when MP3 at 128 Kbps provides around 10:1 compression.
MLP is part of the DVD-Audio standard (not much used) and is used by Dolby True HD (on Blue Ray discs).

Didier

[martyn]

Thanks guys - that now makes sense and it's interesting in itself. Whilst I do have a bit of a mental block when it comes to techical stuff, if explained in simple terms I can grasp it.

Regards,
Martyn