Thursday, 21 August 2008

Mastering Techniques - Using A Compressor - Part 2

This is Part 2 of a series of posts about using compression in mastering - the first post is here. For a more general introduction to using compression, click here.

Choosing the right compressor settings

Now your ears are focused on what the settings are doing, where should you set them ? Easy:

Adjust the controls until it sounds right

OK, that's next to useless, I know. "What sounds right" varies on the instrument or mix, the genre and taste. There is also a big difference between compressing an instrument in a mix and compressing a whole mix.

Compressing an instrument

For example, compressors are commonly used to even out very dynamic (spiky) intruments in a mix, like a snare drum, say. A snare note has a big spike at the beginning (the transient) created when the stick bashes the skin, followed by a longer sustained sound as the body of the drum resonates. If you push this uncompressed signal too high in the mix, the initial transient may start to sound annoyingly loud and percussive or even distort, if you push it into the red. As a result you can't hear enough of the "thump" of the drum to give it weight and impact.

To minimise this effect, you can compress the signal, using:
  • a fast attack time - as soon as the signal starts to get loud, the compressor quickly starts to take effect
  • a high ratio to have quite a dramatic effect reducing the spiky transient
  • a fast release time to allow allow the compressor to "relax" quickly once the spike has been controlled
  • a fairly high threshold so the ring of the drum is not compressed as well as the transient
With a little tweaking, the result should be a much fuller, punchier snare sound - the compressor jumps in quickly (fast attack) and holds back some of the big spiky transient (high ratio high threshold) but because the spike is very short, quickly releases again to allow the main note of the drum to sound. Overdoing it will have undesirable results though - for example if the attack time is too fast, it will remove all the attack from the note, making it sound dull and lifeless. But a bit of experimentation will soon sort this out, and as a result, the snare can be lifted higher in the mix without becoming annoying or distorting - the compression makes it louder. It also sound fuller and punchier, as a by-product.

Compressing a mix

Using settings like the ones above almost certainly won't work well on a mix, though. As a rule in mastering, the aim is for the compression to be as unobtrusive as possible. Usually we aim for a natural-sounding result, where the compression isn't easily noticed. Most final mixes have already had suitable compression used on the individual instruments, so the settings described above will probably result in something that sounds squashed and lifeless, or even pumping and distorted.

Remember in what follows that it's very common to use both a compressor and a limiter when mastering - the limiter catches the very fast transients, allowing the level to be lifted even further, but I'll discuss limiters in the next post. As far as compression goes, for a whole mix I often:
  • Avoid very short attack times - and very long ones
  • Use shorter release times
  • Use low ratios
  • Avoid large amounts of gain reduction

The medium attack time allows percussive elements of the mix to punch through, but still controls the overall signal level. If this gets too long, you'll hear the "thump-suck" effect I mentioned in the last post. Shorter release times also avoid obvious pumping, but you need to be careful. If they get too short, there won't be enough control and you may hear the compressor "bouncing" - rapidly triggering and releasing over and over, sounding crunchy or distorted as a result. Low ratios and moderate gain reduction avoid the compression becoming too ear-catching. Time for another rule of thumb:

If you compare the compressed signal with the level-matched original, it should sound better

Meaning not squashed or pumping (unless that's what you want !). You should always level-match the "before" and "after" levels before making your comparison, of course. When level-matching for comparison purposes, it's often worth using the vocals to judge the loudness. Our ears tend to latch onto a voice as the most important element in a mix, so get these as close as possible before comparing. Then listen and ask yourself questions like:

  • Which do I prefer ?
  • Am I sure one of them isn't louder ?
  • Have I achieved what I wanted ? (ie. made it punchier, fuller, with more impact & excitement)
  • Does the compressed version still sound lively and exciting, or is it too squashed ?
  • Does it sound closer to similar tracks I'm trying to emulate ?
  • Can I hear more of the quiet details in the mix, or is it getting "mushy" and confused ?
  • Does it still sound natural ?

If you can answer these questions with a positive, you're doing well. If not, try varying some the settings and comparing again. If you still can't get a result you like, try a different compressor - or maybe it doesn't need compression at all.

All of this is very hard to describe in words of course, but hopefully by now you'll have a better idea of how compressors are used, what the controls actually do and what you should be listening for.

If you found this post useful you might also like to watch my free webinar on the more advanced technique of multi-band compression - for more information, click here.


Wednesday, 20 August 2008

Rock Music And Gynaecology

An aspect of the mastering engineer's job that is often overlooked is the "people skills" it demands. Often sessions involve meeting artists for the first time, making them feel at ease, gaining their trust, listening and learning about what they want from the session, and then navigating the delicate process of explaining what you're doing with their music and why. All within only a few hours.

As a mastering engineer who is also a musician, recording and mixing engineer, I have a great deal of empathy with both artists and engineers - trying to make a great record can be a demanding, grueling and sometimes emotional process. People often express insecurities about what they've achieved, be it in the performance, recording or mix, and I always try to focus on the positives in what they've achieved, even where there may problems that need addressing. And I hope that I come across as friendly and supportive in the process.

Recently though, the importance of all this was brought home to me even more strongly than usual. Last month I did a really enjoyable session for an unsigned band called the millionstars - gorgeous, quirky, ethereal british acoustic pop with mild electronica influences - cellos, bassoons, beats, breathy vocals and bass clarinet - how could I not love this stuff ?

The session went well and I felt it had been a great success - the recordings and mixes were excellent to begin with, the material was catchy, clever and varied, and in the mastering I was able to add a whole extra dimension of "width" and "gloss" as Rose and Malcolm had hoped I would. We found we had a lot in common as far as our musical tastes were concerned, we had a good laugh, and at the end of the day we all agreed the album sounded great. Job done, and I went home a happy man.

So, imagine my surprise when I was absentmindedly surfing a few days ago and found themillionstars blog, where on 03/07/08 Rose said:

"we went to get our album of songs "mastered" this week. It is a Dark Art... 

...our good friend Mark compared it to calling out to a total stranger in the street to babysit your children. There you go. Perfect. all those tiny fragments of song in your head, the strands of experience, the homespun, uncomfortably, possibly-inappropriately heartfelt lyrics, brought out and recorded and melded together, and then letting them be played VERY LOUDLY to a complete stranger in a room full of boxes and lights. (One word, girls: Gynaecologist...)

anyway!... we have an album. and it feels like us."

Initially I was amused by this, but then I started to feel a bit uncomfortable - Rose was saying I made her feel as if she was visiting a gynaecologist !?!  I'd hoped my "bedside manner" was better than that... so I sent her a slightly worried message, and thankfully she reassured me that I'd misunderstood.

"oh no... it's just the process, letting someone else hear each strand of a song... [a bit] like doing my music exam grades all over again"

And then she added a comment to her blog:

"[Ian] made me feel as comfortable about my voice, bassoon-playing, glockenspiel-mangling and general flouncing-about-on-the-piano as anyone has ever made me feel.
if you're ever considering mastering anything, look him up...  He'll make it sound beautiful, and soothe your soul."

- which has to be one of the nicest things anyone has ever said about me professionally ! So, all was well with the world again. But it reinforces the point of this post:

Mastering engineers need to be sensitive. 

Not only to people's musical intentions and the genre they are working in; not only to their possible insecurities on a technical level as far as the recording goes, but also about the music itself. Even though people often ask me if I like their music, it had never really hit home in quite this way - until I read Rose's comment - that my customers might feel judged by a mastering engineer on an artistic level as well as a technical one. But of course they do ! Often the mastering studio is the first place musicians have their art listened to by someone other than close friends and family or long-term fans - it's natural they might feel uncomfortable, and it's important to be aware of that. Especially since the critical listening environment and constant repetition puts everything under the microscope even more than ever before.

And finally, we need to realise that the mastering session is actually the first step of a new phase for the artist - all their hard work is about to be released for scrutiny, review and criticism by the world at large, and we represent the first concrete example of that. It's up to us to make sure that transition is as comfortable as possible, as well as ensuring that the music sounds the best it possibly can when it arrives "out there".

It's a big responsibility, I hope I can continue to live up to it.

Mastering Techniques - Using A Compressor - Part 1

There are still more things I want to cover in the area of general DIY Mastering, but I've decided it's time to start posting some specific information up here to help people get to grips with common mastering techniques. So this is the first in a new series of posts headed "Mastering Techniques", which will run alongside the DIY Mastering posts. I'm going to cover things like level-matching, EQ, stereo width adjustment and so on, but I think the subject most people struggle with is compression. Often people have been told that the answer to any number of problems is compression, but don't know what they're trying to achieve, or how to get there.

This post started to get much too long, so I've decided to split it into several sections, this is Part 1...

Know What You Want

In my opinion, the most important thing when using compression is to have a clear goal. You'll see lots of explanations of compression saying things like "a compressor reduces the dynamic range of it's input", but I don't find these very intuitive, and prefer the explanation I was given as a trainee:

Compression is used to make things louder

There can be all kinds of positive side-effects of this process, like making things sound fuller, richer, more controlled or punchier, but at the end of the day, especially in mastering, it's all about loudness. NOT excessive loudness, but something musically beneficial.

Mastering engineers almost always use a limiter somewhere to boost level, but the problem with this is that mixes very quickly sound crushed or distorted using only limiting. Using some gentle compression first means the limiter doesn't have to be hit so hard, giving a more natural sound. More on limiters in a later post.

The ideas here apply equally to compressing individual instruments or voices in a mix, incidentally, but you'll need different settings, usually. First we need to recognise a harsh fact of life:

Not all compressors are created equal

The best analogue compressors cost thousands of pounds. However there are some really good software plugins these days which cost far less. For example if you're looking for emulation of a traditional analogue compressor in a mix, complete with "musical" pumping, I really like Sonic Timeworks Compressor X. Would I use it for mastering ? Probably not. However there are high-quality compressors available on a DIY budget which are suitable for mastering - the TC Electronics System 6000 is a mastering "industry standard", and many of it's algorithms are available as plugins for their Powercore system, for example. Many people also use plugins by Waves or Izotope, and discussions rage about whether it's really possible to master with something so cheap, and which is better, on the Sound On Sound mastering forums and elsewhere.

Regardless of which compressor you decide to use though, they all share similar controls and concepts, and at the end of the day it comes down to whether you're happy with the result you get. With that in mind, lets dive in:

Exploring Compressor Controls

Try this experiment - we're going to overdo everything to begin with, so you get a feeling of what the different parameters do:
  • Choose an instrument to compress and solo it (We'll move on to compressing a whole mix later)
  • Patch a compressor across the stereo master output channel of your system
  • Start with a ratio of 2:1.
  • Set attack and release times of 100ms, if possible. You may have to disable "automatic" options first.
  • Gradually reduce the threshold until the meters show you 4 or 5 dB of gain reduction
One of two things will have happened. Either:
  • The sound will have got quieter, because the compressor is holding back the louder peaks. In this case you need to add some make-up gain, sometimes called output gain. Adjust it until the sound is a similar volume to when you hit the bypass or disable switch
  • The sound will already be at a similar level, in which case your compressor automatically boost the output (make-up) gain
Now toggle bypass on and off and listen to the difference. Depending on your material, you will hear more or less difference. If you can't pick anything out initially, increase the ratio to 4:1 or reduce the threshold until more gain reduction is happening. (If you can't hear 6dB gain reduction with a ratio of 4:1 you should probably get your mastering - and probably mixing too - done by someone else !)

If your compressor has automatic attack and release times, it will probably sound OK (but a bit squashed). Even with manual controls, it shouldn't sound too bad. Once you can clearly hear the difference between the bypassed and compressed signals, you can try and figure out what it is you're hearing.

All the controls interact to give different effects, but before we get to that lets look at each in turn. First, ratio and threshold.


Try increasing and decreasing the ratio. Higher values (4:1 etc) cause a more exaggerated effect - the compression "hits harder". Lower values are more subtle. If your compressor doesn't have auto make-up gain, you'll need to adjust it to match the bypassed version for a clear comparison. As a rule of thumb, use a high threshold and high ratio for a hard-hitting sound, but watch out for unnatural results. Lower ratios give a softer, "warming" or "thickening" effect. I rarely use higher than a 2:1 ratio.


The threshold control determines when the compressor starts working. Lower values will give more compression, higher values give less. A low threshold with a high ratio will give lots of hard compression and probably sound very squashed and lifeless, whereas a higher threshold and low ratio will be a much more subtle. Whatever values you decide on, there is one rule of thumb worth remembering:

If the gain reduction meter doesn't return to zero several times a bar, you're almost certainly using too much compression

- because this means that the signal is being compressed all the time, and will probably sound flattened as a result. Try a higher threshold, and then higher ratio if it's not doing enough.

Attack & Release Time

Since I specified long attack and release times, you will probably hear the sound being "snatched" away right after a new note comes in, and perhaps "pumping" back up afterwards. Sustained notes are a good way to hear this. If you increase the attack and release times you'll certainly hear these effects. (For a deliberate example of this classic "thump-suck-relax" pumping listen to "One More Time" by Daft Punk). Automatic or "intelligent" settings reduce this effect, but increase the risk of using too much compression without realising it.

Now try reducing the attack time to it's minimum value. The sound will probably duck very quickly away to begin with - perhaps too fast to hear it happen, followed by the longer release back up to full volume. The chances are it will have lost any impact it used to have, especially with a higher ratio, and sound quite unnatural. Reducing the release time decreases the "pumping" effect, but as you get too short will start to sound "crunchy" or distorted.

Now your ears are focused on what the settings are actually doing, where should you set them ?

Answers in the next post.

Tuesday, 12 August 2008

What is Mastering ?

The art of mastering for CD and DVD evolved directly from the process of "cutting" a lacquer for vinyl pressing, and involves many of the same concepts. But what actually is it ?

Here are some possible definitions of mastering:
  • Creating a production master for replication
  • Achieving an optimal balance of tone and level
  • Gaining the benefit of an experienced, impartial ear
  • Top/tailing and sequencing
  • Fixing any outstanding problems from a mix
  • Making your music sound the best it can be
  • Making it f-ing loud !
So, which one is right? Well, all of them, to varying degrees - except the last one. My favourite explanation is this one:

Mastering is the art of making a collection of tracks into an album (*)

(*) or single, or compilation, or podcast, or catalogue...

This is achieved by one or more of several techniques. As well as technical tasks like ensuring the best transfer from the source and creation of a suitable master, these may include:
  • Level adjustments, often using a limiter or compressor
  • Equalisation (EQ) to achieve a natural, balanced sound - broadly speaking the right amount of bass and treble, but also much more detailed adjustments, for example to remove unnatural resonance or build-up at certain frequencies, or perceptually improve limitations of the mix. Common examples might include adding "air", or "punch", or adding "edge" to guitars, for example
  • Correction of faults - for example removal of clicks, pops or thumps, buzz, hum etc.
  • Detailed sound restoration - usually only necessary on "vintage" sources, can include removal of vinyl clicks, hiss & distortion etc.
  • Stereo image adjustments - this is less common, but may involve widening the stereo image, or (occasionally) adding reverb
Exactly which of these is needed varies from album to album, and even track to track. Some jobs need major surgery, a very few I've ended copying flat from the source. In the later case, did I actually master them? Yes - because I listened carefully, in a dedicated studio using exceptional monitoring, and used my ears and experience to determine that nothing extra was needed. (Actually, more often than not we can spot a source this good within a few minutes of beginning to listen, in which case we contact the artist and offer them the chance of a Direct Transfer instead, so they don't pay for something they don't need.) Deciding to do nothing at all on one or two tracks is just as valid a mastering decision as any other.

However there is still lots of room for confusion and debate. Should mastering engineers:
  • Use the minimum possible processing, and keep everything as close as possible to the original material
  • Preserve the artist's original vision
  • Pull out all the stops to transform a source into what it always "should have been"
  • Preserve the original's dynamic range and impact
  • Use EQ and compression to achieve major increases in level
  • Make everything fit their "trademark sound" ?
Once again my answer is "all of the above" except the last one. This may seem contradictory - surely some of them are in direct opposition to each other ? Not really - because an element of the mastering engineer's skill-set which doesn't often get talked about is intuition. With almost every source I play, I can hear where the artist or engineer was "trying to get" within minutes or seconds. I can hear what they're trying to achieve, and I see my job as trying to help them get there. Using minimal processing, if possible but if not by throwing the kitchen sink at it, and all combinations in between - always staying true to the original mix.

The issue of levels and compression is a good example of this - there are lots of easily available limiter and compressor plugins now, but many of people complain that they ruin the sound. Mastering engineers use very similar tools to achieve their results, and claim that they make things sound better. How can both be true? Partly because there is still a distinction between the tools - mastering studios typically spend thousands of pounds on a single compressor, whereas for the same money you can buy an entire suite of plugins - but also because we are constantly honing our skills to use the tools transparently, and our listening environment to be able to hear when it's working. To some extent, the skill of a mastering engineer is to achieve an appropriate level for every track , sometimes reducing the dynamic range in the process, but make it sound as if the final result is actually more dynamic. Or to make major EQ adjustments, without changing the essential qualities of the original.

So, you might ask - what's the point of paying for something that can be so subtle ? There are several answers to this:
  • Often it's not that subtle ! If I'm doing my job, the mastered version will simply be better than the original, while retaining everything that was good about it.
  • Where the difference is less obvious, it will only be difficult to hear when level-matched. The importance of increasing the level of a track to it's own particular "sweet spot", without pushing it over the top, is hard to over-emphasise. Doing this for all of the tracks in an album, and getting them balanced perfectly against each other in their final sequence is even more important and valuable. This needs to be done with great care and skill though - it's almost impossible to achieve this simply by pushing the level up into a plugin.
  • Ideally, the differences should be subtle. A truly great mix only needs the slightest of tweaks, but even these minor adjustments, over the course of a whole album, add up until the sum is greater than the parts.
As I type this I'm struck again by the inherent contradictions of the job. It requires you to be entirely humble - I start every session by listening carefully to the source and thinking "what's good about this ?"; but also supremely arrogant, making changes to a mix that someone has sweated blood over for perhaps weeks or months. It requires deep technical knowledge, but many of the judgements made are largely aesthetic and artistic. It means knowing when something ain't broke and not trying to fix it, but also knowing when to roll up your sleeves and get your hands dirty...

What is mastering ? Has this post helped explain it at all ? Who knows...