oceantracks
Thread Starter
#1
25th April 2010
Old 25th April 2010
  #1
Lives for gear
 
oceantracks's Avatar
 

Thread Starter
MP4 vs WAV

Can someone explain the difference in quality between an MP4 and a WAV file? I did some searches, but mainly come up with MP4 converter software and one WIKI article on MP4s....

Just curious about any quality differences...

Thanks
TH
#2
25th April 2010
Old 25th April 2010
  #2
Lives for gear
 
ray dsr's Avatar
 

huge differences.
i'm sure some tech-heads will chime-in with the details, but WAV files are uncompressed, full-res files that can be very quality. MP4 or M4A files are lossy formats to make the original files much smaller.
#3
25th April 2010
Old 25th April 2010
  #3
Gear addict
 

As a simplification, AAC (MPEG-4 Part 3) and MP3 (MPEG-1 Layer 3) encoders both reduce data rates compared to WAV by throwing away frequencies that we're less likely to hear, as well as encoding audio in such a way that noise increases which also reduces data rates. There are more complicated bits, but I suspect that's as much as you want to know. There are also some lossless, reversible parts to both codecs.

It's not strictly true to say that AAC is lower quality than WAV. It's true in the sense that, if you encode a WAV to AAC, you will lose some information, but if you tried to make a WAV as small as an AAC it would sound much worse. For example: try comparing a 44.1kHz 128kbps AAC from a 24-bit source to a 16kHz, 8 bit WAV file and let me know which one you prefer. They're both the same size, give or take.

It's generally thought that AAC offers better quality than MP3 at the same bit rate, but that's not always true and depends on the encoder used. Encoders are changing all the time and hopefully improving. The idea is to throw away as much inaudible information as possible, and then the least audible information. In some cases it's possible to make an AAC file that's perceptually identical to the source file, and in some cases it isn't.
#4
27th April 2010
Old 27th April 2010
  #4
Lives for gear
 
DistortingJack's Avatar
 

Post

mp4 or m4a is not a codec, it's a file extension which can refer to several different underlying codecs. The most common ones would be aac and apple lossless.
So technically a m4a could be a lossy file or a lossless one.
If you know your way around image files a little bit, you'll get this analogy:
wav is like bmp. Originally windows but now a standard everywhere. Uncompressed and lossless.
aif/aiff is like tiff. Originally mac but strictly equivalent to wav. They are both uncompressed and lossless.
mp3 is like jpeg. Lossy, and a bit shit at high compression rates, but can be quite decent at high quality settings. Compressed and lossy.
aac is like jpeg 2000. Slightly better than mp3 but still lossy and less compatible. Compressed and lossy.
FLAC and Apple Lossless are like PNG. It's a form of compression (think WinZip) which throws away redundant data but can recover it through rather advanced mathematical algorithms. They will make your files smaller (both are roughly equivalent, 50 to 80%) but you will be able to recover 100% of the information at the time of playback. Main drawbacks are processing power required and compatibility problems (FLAC doesn't play nice with iTunes, Apple Lossless doesn't play nice with anything but iTunes). Compressed and lossless.

Now, the file extension is not always an indicator of the codec used. Like AVI or MOV or indeed MP4 on video files, there are several formats that have the same file extension, namely aac and apple lossless for audio. If you have an m4a file, it can be either of those. Of course to check, you just need to look at the bitrate. Under 320kbps it's aac and thus compressed, above that its Apple Lossless.
mp4 as an extension can be either video or just audio. If it's just audio it's equivalent to m4a, if it's video it's equivalent to m4v.


I haven't had any tea this morning so it might all be bollocks.

Hope it helps.
soulstudios
#5
27th April 2010
Old 27th April 2010
  #5
soulstudios
Guest
 

Agreed except that 99% of cases MP3 is better than AAC, if you use a decent encoder. AAC is "technically" a better specification, in reality though Apple's encoders are rubbish, and a lame-encoded mp3 is always better than an AAC file (you can turn off lowpass filtering for both).
(and also it's not FLAC that doesn't play nice with iTunes - it's the other way around - because apple want their lossless proprietary format to win)
Cheers,
M@
#6
27th April 2010
Old 27th April 2010
  #6
Lives for gear
 
MonkeyAdam's Avatar
 

Apple Lossless Audio Codec will have an m4a extension. These sound very good from my experience, but it can't handle 24 bit 96 kHz like FLAC. Now that's a badass codec. I've recently been downloading high res FLAC files from HDTracks.com. They sound amazing.

To encode FLAC you can get xACT or look it up on sourceforge.
#7
27th April 2010
Old 27th April 2010
  #7
Lives for gear
 
DistortingJack's Avatar
 

Quote:
Originally Posted by MonkeyAdam View Post
Apple Lossless Audio Codec will have an m4a extension. These sound very good from my experience, but it can't handle 24 bit 96 kHz like FLAC. Now that's a badass codec. I've recently been downloading high res FLAC files from HDTracks.com. They sound amazing.
Apple Lossless doesn't sound very good. It sounds exactly like what you put in. I just checked, it does 96k 24 bit too.
I tend not to worry between FLAC and Lossless. If I really need to, I can batch convert all my lossless to FLAC in a night, without any loss of quality. It's the same.
#8
27th April 2010
Old 27th April 2010
  #8
Gear addict
 

Quote:
Originally Posted by soulstudios View Post
Agreed except that 99% of cases MP3 is better than AAC, if you use a decent encoder. AAC is "technically" a better specification, in reality though Apple's encoders are rubbish, and a lame-encoded mp3 is always better than an AAC file (you can turn off lowpass filtering for both).
There are no absolutes like that in lossy coding. Some audio causes problems in Lame's MP3 that are not there in Apple's AAC, and some are the other way round. You may well be right that MP3 generally outperforms AAC despite having an inferior specification—I haven't done enough testing to know either way. Spotify using Ogg Vorbis doesn't sound bad, either.

Disabling low-pass filtering means that bits that would have been used to encode the (more important) mid-range frequencies are used to encode the (less important) HF frequencies (17k plus, or thereabouts). So the frequency response may "look better", but at the expense of accuracy in more easily audible parts of the spectrum. Developers have spent a long, long, time tweaking presets to make them as good as they can be for a given bit rate. Any (simple) tweak like that that any end-user can think of has probably been tried before many years ago.
soulstudios
#9
27th April 2010
Old 27th April 2010
  #9
soulstudios
Guest
 

Quote:
Originally Posted by haberdasher View Post
There are no absolutes like that in lossy coding. Some audio causes problems in Lame's MP3 that are not there in Apple's AAC, and some are the other way round. You may well be right that MP3 generally outperforms AAC despite having an inferior specification—I haven't done enough testing to know either way. Spotify using Ogg Vorbis doesn't sound bad, either.

Disabling low-pass filtering means that bits that would have been used to encode the (more important) mid-range frequencies are used to encode the (less important) HF frequencies (17k plus, or thereabouts). So the frequency response may "look better", but at the expense of accuracy in more easily audible parts of the spectrum. Developers have spent a long, long, time tweaking presets to make them as good as they can be for a given bit rate. Any (simple) tweak like that that any end-user can think of has probably been tried before many years ago.
Yeah yeah yeah... but one of the many tweaks that AAC trumpets is a lack of lowpass filtering... which is why some audio afficionados claim better quality - so I was just pointing out that lame does the same...
and actually, some files do some better with filtering turned off -
but it depends on the material.
It's extremely unlikely that you will be able to find an audio example where apple-encoded AAC outperforms lame-encoded mp3- hence- 99%.
Cheers,
M
#10
27th April 2010
Old 27th April 2010
  #10
Gear addict
 

Quote:
Originally Posted by soulstudios View Post
Agreed except that 99% of cases MP3 is better than AAC, if you use a decent encoder. AAC is "technically" a better specification, in reality though Apple's encoders are rubbish, and a lame-encoded mp3 is always better than an AAC file (you can turn off lowpass filtering for both).
(and also it's not FLAC that doesn't play nice with iTunes - it's the other way around - because apple want their lossless proprietary format to win)
Cheers,
M@
From my personal experience I couldn't disagree more.

Very rarely will I listen to an MP3 and be happy with it (regardless of whether or not I know it is MP3).

On the contrary, rarely will I listen to an AAC and be uncomfortable with it (regardless of whether or not I know it is AAC).

This goes for files given to me by others and files converted by me (through whatever process).
#11
27th April 2010
Old 27th April 2010
  #11
Gear addict
 

Quote:
Originally Posted by soulstudios View Post
Yeah yeah yeah... but one of the many tweaks that AAC trumpets is a lack of lowpass filtering... which is why some audio afficionados claim better quality - so I was just pointing out that lame does the same...
and actually, some files do some better with filtering turned off -
but it depends on the material.
Fair enough. If you're being paid to create the best quality possible then it is sometimes worth spending some time choosing the best settings for the specific case. What I meant to say was that, if you're just running off a rough ref for something or encoding your entire personal CD collection, then it's not really worth the time and effort second-guessing the presets each time.

Quote:
It's extremely unlikely that you will be able to find an audio example where apple-encoded AAC outperforms lame-encoded mp3- hence- 99%.
Cheers,
M
Yes, that's my reading that's at fault then, if I'd paid more attention to what you'd written I'd have realised we're mostly in agreement!
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Similar Threads
Thread
Thread Starter / Forum
Replies
no ssl yet / Music Computers
5
piano / Music Computers
8
Kris / Gearslutz Secondhand Gear Classifieds
8
cebolao / Music Computers
0
claudemorrow / Gearslutz Secondhand Gear Classifieds
7

Forum Jump
 
Register FAQ Search Today's Posts Mark Forums Read

SEO by vBSEO ©2011, Crawlability, Inc.