Audio file formats - recording and storing


compact_discCD (Compact Disc), our first mass digital format, arrived with us over 25 years ago. It gave us clean digital sound in a way we hadn’t experienced before. There have been new HD audio disc formats introduced over the years (SACD), but CD was so well established they’ve become rare items.

In 1993, with the computer revolution well underway, MP3 was introduced to enable music to be stored relatively easily on a hard disc. A 3-minute CD track represented a raw ‘PCM’ file of about 60mB, whereas a MP3 file was only 3-5mB, allowing over 10 times the media to be stored.

So how does MP3 achieve this? As well as applying a mathematical formula to the raw PCM data to reduce its size, it applies what is called ‘Auditory Masking’. If a loud sound happens at the same time as a quieter sound, it decides not to record the quiet sound as it’s ‘Masked’ by the louder sound as you can’t hear it. Basically in recording an MP3, it has decided for you what you can and cannot heard and discards the information it feels doesn’t matter.

When I first heard an MP3 file played back on a decent Hi-fi (an orchestral track), I was at first quite impressed. It sounded as if the Orchestra had been closed mic’d rather than a simple microphone pair slung overhead. But as I listened I began to feel something was wrong. It took me nearly 5 minutes to work out why……. There was no hall!!!! There was no acoustic on the recording – the hall reverberation had been removed by the processing, making it quite a dry recording. If you listened very hard you just make out the dying reverb simply vanish at a given point.

Back in 1993 the average PC had just 32mB of RAM, a CPU speed of 60Mhz and the biggest ‘industry’ hard drive available was just 1Gb. The Internet was in its infancy and you would have to wait a few years till you could achieve 56k on dial-up!  We now have RAM size, CPU and broadband internet speeds in the Giga bits and hard drives in the Terabyte (1,000gB)!

With all this space and speed it seems crazy that we’re only just beginning to use CD raw quality PCM files on our computers (WAV & AIFF), such has been our preoccupation with the MP3 format.  Plus Blu-ray now gives us uncompressed audio 5.1 soundtracks with our films.

There has been a myth that has pervaded over the years that ‘Digital’ is perfect and once you are in the digital domain (i.e. on a computer) then deterioration of quality is a think of the past – don’t believe it!!! And especially if you start converting between file formats - There will be degradation!

So record in a raw format and stay with it right through the production process if possible. If you’re recording the audio to camera then HD format cameras give you the best sound file formats.

MP3 has served us for a long time, it just seems amazing its taken so long to return to an audio quality first achieved over 25 years ago.

Incidentally, the only time I can see the use of MP3 as a recording format is in a ‘news’ type situation, where you haven’t got long to record your interview and there’s a noisy background – the MP3 processing may help you lift the speech clear of some of the background noise, but then again perhaps you should look to record it properly!!!

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Many thanks for you patience.
Kind regards,
Mike - Media4ed.

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