Saturday, March 30, 2013

iTunes makes broken MP3 files now?!

I've always stuck with MP3 files for music because it is the only format that everything we've ever owned will play. Currently we've all got iPhones and iPods but the car machine is one of those no-name head-units that's a radio and a flash-memory player. In the past we've had an assortment of 'phones and no-brand MP3 players and so I think the choice I made back in the late nineties to start moving all my music to MP3 was valid.
People object to MP3s for one of two reasons;
  • It's not an open format like OGG Vorbis - it's notionally "owned" by Technicolor. It is so ubiquitous that I suspect they'd have problems enforcing that.
  • It's lossy, and not even the best example of a lossy codec.
As ever Wikipedia has a very comprehensive article. On the first point I think life is too short to get all religious about technology choices. In the case of documents formats - sure; send RTFs rather than DOCXs just for politeness (actually, both formats belong to Microsoft!). Not everyone has the right machine or can afford MS Office (oh, and NEVER send Open Office specific files!).

In terms of the lossy nature of MP3s I'd say that if you encode files well yourself it shouldn't matter for most people and most music. With very little effort you can get MP3s that are so close to the uncompressed data that came off the CD that you'll never know. Audiophiles (who still tolerate all the noise and 2nd order harmonics that come off vinyl - and don't get me started on the RIAA characteristic!) claim that no compression is good, but I suspect they do so for reasons of fashion or self-aggrandisement. The reason I say that is I have actually done the tests!

Back in 1999 I was involved in a project to transfer a large audio sound effects library to a server. The start of the project was to see how well compressed audio was suited to the task. Drives were small and expensive back then and so the success of the project rested one us using compression. So - we compressed several dozen bits of audio to 96, 128, 160, 192, 256kbits/sec;
  • Spoken word - properly recorded in a high end audio booth for existing TV voice-overs, male & female.
  • Music - a selection of acoustic, classical, rock etc
  • Sound effects - from the BBC library, spot effects as well as longer ones (bird song etc)
So these were blind-played to the Oasis Television audio staff (at the time a good example of "golden ears" - people who have been trained to hear audio problems) in properly built audio suites (£10k speaker systems in acoustically dead rooms). So - not amateurs making judgements on sub-£1,000 domestic rigs, but a proper blind-test using professionals.

What we discovered was that past 256kBits/sec nobody could get reliably better than 50% correct - it was as good as if they were guessing which was compressed and which was uncompressed. This seems to fly in the face of current opinion that says that even 320kBit/sec is detectable on iPod earbuds (!) - and don't forget that the LAME and Fraunhofer compressors (reckoned to be the best) have been getting better over the last decade-and-a-half (particularly with respect to VBR encoding).
Lots of people also suggest that other codecs (particularly AAC and WMV) are now better than MP3; I've never been able to hear that when I've compared like-for-like (data rate, VBR vs CBR etc) and since MP3 is so ubiquitous it seems likely that manufacturers would have spent more dollars optimising it that any of those lesser used codecs?

So - I compress my music to 192kBits/sec using the LAME VBR setting and I rarely hear an artefact. There are a few albums I did back in 1999 that I've gone back to because modern compressors are so much better and the little MP3 player I had back then could only hold a complete CD at 128kBits! The cruel irony is now that I know what I'm listening for and can (just about!) afford decent speakers my hearing response is rolling off quite markedly. Pretty soon AM radio will sound good. I've also found that when I mix live music I drive the high-end a lot more than I used to and that must be the same effect.
There is another effect that people talk about - how tired you get listening to compressed audio - the brain doesn't like artefacts that you don't encounter in nature. I think this is true, but the people who make play of it tend to be vinyl & FM radio fans - both of which are covered in very unnatural artefacts.

So - to the point of the post; I discovered that a couple of CDs encoded by iTunes over the last year wouldn't play off a USB stick in the car. I had to re-encode them on the old AltoMP3 maker software I used to use. flailing around online seems to suggest it's the way Apple sticks artwork in.

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