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Squeeze box – mastering for MP3

How to master with phones, iPods and other MP3 players in mind, with Fluid Mastering’s Nick Watson

With more and more releases inevitably finding their way onto iPods, laptops and other MP3 players of every imaginable complexion, shouldn’t this compressed file format be considered when mastering to CD? Mastering engineer Nick Watson points out the pitfalls… Why is this an issue?

“Every commercial release goes onto CD but is available as a download, so the mastering ends up being the same version. Sometimes they’ll just take the CD master and work from that. Sometimes they’ll ask for a separate copy, but the audio is essentially the same.” So there’s no separate process where you say, right, now let’s do the download master?

“No, there isn’t. And if you are mastering something loud, and you get into a situation where there’s some distortion – even if it’s not really audible on CD – you are creating signals within the spectrum that might not encode very well. When you clip a signal, you are essentially creating additional harmonics – high frequency ‘garbage’ that will hamper the encoding process, to an extent.” And that’s because it’s a process of reduction that can’t handle those dimensions?

“Yes, you’ve got a limited bandwidth on MP3 and you don’t want to be using it up by encoding stuff that is not integral to the sound.” How does that manifest itself?

“The vagaries of MP3 are that every single mix will end up suffering in a different way. You’re throwing away quite a lot of information when you downgrade to MP3, and how that appears will vary from one track to the next. When MP3 first appeared we were asked to encode an entire catalogue, so we tried out lots of different MP3 encoders to find out which was the best one. Basically, there wasn’t a best one – what worked on one track wouldn’t work on another one.” Why is that?

“It’s a psycho-acoustic issue: the compression works on the basis of how we perceive sound, whch is why it’s so subjective and variable.” How do you avoid such vagaries?

“Avoid clipping distortion. Having too much level generally is not a good idea on MP3, but the problem is that we are often asked to master at very high levels. That could be an A&R request, but these days it’s just as likely to be the bands themselves asking for it, as it were. The industry wants impact from its products, and we can do that, but at the same time we could be creating a situation where the general public is consuming horribly distorted material all the time and, quite possibly, is getting used to it. Whether that is reflected in a reduction in the number of sales is impossible for us to say. There’s no way of measuring that accurately. But anecdotally, it seems that a technical shortfall is being noticed – at least within the industry.”