DIY Mastering Part 4 - Mastering Speakers and Monitors

The most important tool a mastering engineer has (apart from his ears and expertise) is the monitoring, meaning the speakers, amps and converters. We debate all of these at great length between ourselves, in online forums and down the pub, but without question the speakers have the greatest impact on the sound. (They need to be well-placed in a decent treated room, but I already covered that in my third DIY post.)

This post won't enable you to choose a set of speakers by reading specifications or manufacturer's blurb, but hopefully it will give you an idea what you should be looking for, and why.

So, what are suitable speakers for mastering ? Well for example we have B&W Matrix 801s in Studio 1 at SRT, Genelec S30Ds in Studio 2 (In general I don't rate Genelecs, but the S30s have a ribbon tweeter and are in a class of their own). Other common names include ATC, PMC and Dunlavy. What all these monitors have in common (apart from costing at least as much as a large family car !) is that they have:

1. Flat, or neutral frequency response - meaning their response is very even over the whole audible range. So, for example, B&W 801s come with a graph measuring their response - it only varies by +/- 1 dB from 20 Hz to 20 kHz.
2. Acurate phase response - meaning that the stereo image is very detailed, giving an absolutely solid mono center image, but also a deep, convincing "three-dimensional" soundstage - at least, on a decent recording. The stereo imaging in our studios is so good that it's common for people to ask if some of the sound is coming out of the center speaker (used for surround work), even though they are listening to pure stereo. And on the occasions where a mix element is accidentally phase-reversed, it leaps out and draws attention to itself.
3. Clean, controlled dynamics - with only minimal distortion introduced, even at high listening levels. (Using a suitable amp is important for this, too, of course.)

Of course there are many other aspects of speaker's capabilities I could list, but it's almost more important to realise that these characteristics mean mastering speakers should be:

1. Revealing - allowing you to hear details you'll miss on other speakers - faults, like clicks, hiss and distortion; but also the positive sides of the recording - accurate stereo imaging, "depth" (meaning the impression of a three-dimensional sound field), impact and dynamics. Listening on a mastering system should almost be like wearing headphones, in this respect.
2. Clinical - Mastering speakers don't make things sound good. Unlike speakers for tracking or mixing, they shouldn't add "vibe", or "feel". Often they might be described as "bland", "boring", or at best "civilized". In fact, they are reliable and acurate. Only the very best recordings will sound good on them ! In fact that leads us neatly to:
3. Unforgiving - It's often shocking to hear how bad many recordings sound on a mastering rig - the uncompromising accuracy uncovers limitations masked by lesser reproduction systems. While this won't necessarily make for a very satisfying listening experience, it's essential for the mastering engineer to hear and correct any problems or limitations in the original mix.

Together, all these requirements add up to help the engineer achive translation - when it sounds it's best on the mastering system, it will sound great everywhere else, too.

So, if you've got this far, you're probably thinking "how the hell do I choose speakers which meet all those criteria ?". If you can't rely on printed specifications alone, this is a tough question. Until you're learnt exactly what a recording should sound like, it's hard to recognise a pair of speakers that make it sound that way.

Probably the first piece of advice is to get some recommendations. This post was inspired by a thread on the Gearslutz mastering forum asking about mastering speakers, and places like this or the SOS forums are good places to start - perhaps less than £500 isn't really realistic, though! Several of the speakers I mention above are available second-hand for "reasonable" amounts of money. My personal favourites, B&W, have ~35 staff working constantly on research and development, and the advances they make for their most expensive speakers always filter down to the cheaper models. I have Series 2 601s at home and am frequently amazed by how good they sound. Not that I'm suggesting you use them for mastering, but considering the difference in size and price, there's almost certainly something in the 600 range to suit.

Next - listen ! Find a showroom where you can test a few different speakers, ideally in the same room, and listen to various different tracks you know well. Even better, get some on demo and try them in your room. Remember you're looking for accuracy, not excitement - mastering monitors reveal limitations that others don't. Choose a range of recordings and be objective. "Sledgehammer" by Peter Gabriel is a great-sounding track, but it has very tight, controlled bass, so if the speakers give it a thundering bottom end, they aren't flat. "Dummy" by Portishead is a classic album, but it's almost entirely in mono - that should leap out at you. Maybe even take a CD with a few test-tones on it - for example a sine wave sweeping up from 20Hz to 20kHz will not only give you an idea about the speakers frequency response, but may also reveal a few buzzes and rattles along the way. (Don't play it too loud, though, or you may find yourself paying for some blown tweeters...)

Finding the right speaker in your price-range is a major challenge for a would-be DIY mastering engineer, but once you've worked with truly acurate monitoring for a while, you won't want to go back.

DIY Mastering Part 3 - Room Acoustics, Treatment and Layout

This is too huge a subject to cover properly in a blog, but if your monitoring environment isn't working well, you'll never be able to make good mastering (or mixing) decisions, so before you start considering tools or techniques, you'll need to get the room working reasonably well. Here I'll try to give some short but useful pointers and links to good, more detailed information.

The Room:

1. Needs to be a decent size - at least 3m x 4m, say.
2. Needs to have good proportions. Square is bad, a rectangle is better unless it is twice as long as is wide. All shaped rooms have "nodes" - certain frequencies which are emphasised or minimised by reflections between the walls. The dimensions of the room determine which frequencies will be emphasised, and the goal is to spread these nodes out as much as possible, to give the most even response. There is a great free utility called ModeCalc which allows you to calculate the room nodes for a given room, and the same page has a great introduction to the subject. Ideally, you could build "splayed" plasterboard walls to give a wedge shape which reduces the nodes even further.
3. Needs acoustic treatment. Every room will benefit from some acoustic panels - you can make these quite simply yourself using high-density fibreglass ("rockwool") mounted in wooden frames, or buy them from a company like RealTraps, who run the site that the ModeCalc utility is hosted on. These "bass traps", or more accurately "broadband absorbers", will further even out the frequency response of the room, enabling you to make better mixing and mastering decisions. Foam panels may also be helpful but are far less effective, especially in the bass end, where rooms have the most problems. Egg-boxes are useless !
4. Needs the speakers in the right place. They should be on a shorter wall, not too tight into the corners, equally spaced from opposite walls. I've seen several very theoretical methods of determining this, but perhaps the best advice is to get a recording you know well, play it at your chosen reference level, and move them around till they sound "right".
5. Needs a good listening position - equally distanced from both speakers, obviously, but not in the middle of the room. Whatever the shape, some bass frequencies will cancel most strongly in the middle of the room, so it's almost always a bad mix position. If you are one third of the room length away from the speakers, you'll be off to a good start.
6. Needs the right materials. For example, Pro studios use very expensive acoustic panels to control the sound by reducing unwanted reflection from smooth plastered walls. A cheaper alternative is to put carpet on the walls, with the idea of "deadening" the sound. However this isn't always a good idea in a mastering room - since the idea is to get the best possible result for a "normal" listening environment, a certain amount of reflection in the room is important, otherwise you'll be tempted to add too much high frequency to everything. Heavy curtains are probably a better idea for controlling the "liveness" of the room, not least because you can easily change their arrangement and effect on the sound in the room.

All of the factors above affect the way your room sounds, hopefully for the better ! In a later DIY post I'll describe a few simple tests to help you check if your room sounds good.