This is Part 2 of a two-part series by UK mastering engineer Ian Shepherd, who runs Mastering Media and the Production Advice website.. Check out part 1 here.

6. The Gaps don’t work

People usually fall into two camps – when you say “right, lets do the gaps”, they’re either the ones who say “huh ?” and look confused, or the ones who say “OK then!” and get out their notepads : )

Once you get into it though, everyone sees the point – and usually they agree on what the perfect gap is between any two songs ! Gaps play a crucial role shaping the flow and feel of an album. If a gap is right, you’ll never even notice it’s there – if it’s wrong, it’ll stick out like a sore thumb.

Take a little time to get the gaps right. To help you, here are my two favourite rules of thumb to try:

  • Roughly two seconds from when the first song “feels” like it’s finished.
  • Two bars from the end of the first song, at the out-going tempo

7. Sample rate disasters

This problem can occur without you even knowing it.

It doesn’t matter what sample rate you recorded at – CDs need to be 44.1 kHz. So the final stage of mastering for CD should always be to convert to that sample rate. You need to be careful though – not all sample-rate conversion (or “SRC”) is as good as it should be. Symptoms of poor conversion can include metallic-sounding “aliasing” distortion or harsh, gritty added noise.

You can see a comparison of many different sample-rate conversion options here:

SRC Comparisons

The good news is that there’s a free piece of software called Audacity which gives excellent results – if your DAW doesn’t have graphs that look similar to it’s results on the page above, it might be better to use Audacity instead. Wave Editor also has superb SRC options too, if you use a Mac.

8. No dither

This is a subtle but also very common problem. Dither is a very low-level noise signal added to the audio to remove quantisation distortion when processing. If the audio isn’t dithered properly, you can end up with subtle but nasty distortion – it makes things sound edgy, brittle and “glassy”. In fact, I sometimes think many people’s adverse reaction to digital audio in general when it was first introduced may have been a reaction to dither problems, as much as anything.

Now, most DAWs use floating-point processing these days, so if you work entirely within one piece of audio editing software, you don’t need to dither until the very last minute when converting to 16-bit for the final CD burn.

If you’re moving between different audio applications though, I recommend using dither whenever you do. Not a fancy “noise-shaped” dither, as multiple layers of these can sound unnatural – provided you’re working at 24-bit, any simple dither will do.

So to summarise – at the final stage when you’re reducing to 16-bits, make sure you remember to dither. Many burning applications do it for you automatically, but it’s an important detail to check.

9. Missing Metadata

Metadata is extra information stored within different audio file fomats. CDs have only very limited metadata options – track titles, artist name and title are all included in the “CD Text” information, plus barcode (EAN/UPC) and ISRC codes.

mp3 files support a much larger range of information though, via the ID3 tag. There’s a great post on mp3 meta-data here:

7 Steps to metadata utopia

Of the options on CD, ISRCs are probably the most important – these are unique codes which allow your music to be automatically logged for royalty payments by any system that supports it – for example, radio play.

(CD Text is only supported by a few players, and doesn’t affect track names in iTunes, Windows Media Player etc – these need to be submitted separately, online)

10. Messed-Up Masters

The final stage in the mastering process is often audio files, nowadays – mp3s, FLAC, AAC, WAV, AIFF – the list goes on. And if your dustribution is online only, then getting a good master simply means exporting those files at the best quality you can, and making sure they include all the metadata you need.

If your mastering process includes CDs though, there are a few more factors to consider. A CD isn’t necessarily a guarantee of perfect reproduction, unfortunately.

High error rates and poor-quality burns can cause problems in players, or for masters to be rejected when you submit them for duplication. In the worst case, you may even find the audio data is changed on the final copies.

Here are the main factors to consider:

  • Use decent quality media – Taiyo Yuden usually give good results and are available from Amazon
  • Don’t burn at very high speed – go for the lowest speed listed for your media. So if it’s listed as 8x-24x, burn at 8x. This usually gives the best results.
  • Don’t use adhesive paper labels – these can cause the disc to spin unevenly and reduce burn & playback quality
  • Always check to the final master – you never know when a glitch or click will have crept in. Never send out a master without listening to it all the way through on high-quality headphones
  • Keep the master clean – always handle the disc by the edges, and straight after the final listen, seal the packaging so it can’t get scratched or dirty

You can avoid many problems with CD masters completely by supplying them as DDP files, incidentally – but that’s a whole other blog post !

So there you go – my top ten mastering mistakes, and how to avoid them ! I hope you find them useful – if you think I missed any, please let me know in the comments.

A big part of mastering is multi-band compression, if you want to learn more about it from Ian himself, check out a free video we put together at www.multibandcompression.com.

  • Great article! I read somewhere recently that dithering is only important for physical CDs, and not for digital only releases (download or streaming). What are your thoughts on this?

  • Madman

    “Don’t use adhesive paper labels – these can cause the disc to spin unevenly and reduce burn & playback quality” don’t know if i completely understand that one. what other kind of labels are there?

    • Hmm…I think he’s referring to actually printing on the disc versus actually sticking a paper label on it.

  • Jon

    Hi Joe

    Loved your free eBook and will be putting up a link shortly on my blog..many of my readers are interested in home recording and your eBook sounds like the perfect place to start.

    Many thanks again
    Jon
    WirelessSpeakersHub.com

  • Raphael Cassis

    Nice posts indeed, Joe, thanks…
     
    In the SRC Comparisons website you put there I can find a “Apple CoreAudio (Leopard)” which presents a great performance too, better than Logic 9 at least. Do you know how to make this type of sample rate conversion?

    • Hi Raphael,

      That’s the result you’ll get if you do the conversion in an app that uses the CoreAudio routines – I don’t know for certain but I imagine opening a file in the QuickTime 7 Player and saving at a different rate would do it, for example.I’m always cautious about this kind of thing, though – I prefer to go with a “known quantity” like Audacity.Ian