Figure 1: If you're using MIDI Controllers to automate volume levels for expression purposes, make sure you're using the full range of control, to minimise noise. The upper window shows a string part using all the Controller 7 (Volume) range. The lower one may be adding more noise to the mix than it should, simply because it never goes above half volume therefore requiring more input gain.
Setting up MIDI gear for the best audio quality is a very similar process to setting up your mixer, and you can often reduce noise levels significantly. Martin Walker provides some quick and easy ways to minimise hiss and hum from MIDI gear.
It's vital to set up your mixer gains carefully, so that your music is sitting neatly in that optimum area between noise at the bottom and distortion at the top, as I explained in the April '98 issue of SOS. But MIDI signals can also benefit from a little preparation in this area. Modern keyboards and synth modules tend to be fairly quiet (although you rarely see specification figures), but most people have at least one older device that's a bit noisy, and anyone using a computer soundcard may well have computer‑generated burbles in the background, courtesy of the many interference‑generating components inside the average computer casing.
Many people adopt a fairly fixed way of working, depending on just how many MIDI devices they have. Most of us start out with one synth, which is likely to be called on to play back half a dozen or more different sounds at once. Fortunately, most modern synths have generous polyphony, but often many of the richest sounds tend to use two or even four oscillators for each note played, which causes this polyphony to plummet. However, with careful management, note stealing (where an older note is suddenly cut off to make way for the most recent one if there are no more spare notes available) can be a thing of the past, and it's perfectly possible to create an entire song using a single MIDI module or keyboard.
Once you have two or more synths, the number of notes you require each to play will start to drop, as you are able to become more selective in choosing your sounds. You may find that certain synths are only playing back a couple of sounds, or even a single monophonic melody or bass line. Sometimes the most interesting sounds are created by layering similar patches from different sources, so that you're effectively using several synths to generate one composite note.
Most MIDI devices have default internal levels that are suitable for playing back an entire track by themselves — this is fairly obvious from the built‑in demo songs. Normally this means somewhere between six and 16 channels on the go at once, and therefore a high overall output level. However, if you're only using a couple of notes, the overall output level will drop considerably. When a synth is plugged into a mixer line input it's not unusual to find that playback of a GM file needs the gain switch set to +4dBu (low sensitivity), but when using the same MIDI device as one of a set in a typical studio, you could well have to increase the sensitivity to the ‑10dBV position.
As you might expect, playing back just a single note on a module designed to output a dozen or more sounds may compromise noise level, but there are plenty of little things you can do that should improve this. Remember that withless coming out of each module you also get more opportunities to add individual EQ and effects via your external mixer, which can give better separation in the mix.
Tweaking your synth patches to achieve maximum volume without distortion can improve sound quality.
Quick Tweaks
Figure 2: If you can't get high enough MIDI velocity values from your keyboard, you could use an 'Input Transformer' function, such as this one in Cubase to add a fixed amount to the velocity of each note as it is being recorded (so that you can hear the effect in context using MIDI Thru).
The first thing to check is that the physical volume controls on all your MIDI synths are turned up full. If you listen to the background noise coming from most synths when they are not being played, it changes little with the position of this control, but the level coming from the synth does. Turning this control up full will give you the highest output level compared with background noise, and therefore the cleanest output signal.
For a quick improvement in MIDI noise levels, identify the worst offender first. Set up a typical mixer routing for one of your tracks, with all the MIDI devices set to sensible fader levels, and then, without actually playing back a MIDI sequence, turn your monitor volume up high, and listen to each MIDI mixer channel in isolation to hear its noise contribution (make sure you use the Solo or PFL function on your mixer, so that you're only listening to this one device). Once you've identified the worst offender, use the other tips here to deal with it — you may find that this gives you a significant improvement by itself, which should inspire you to carry on until your MIDI system is fully optimised.
This may seem like a slight diversion, but while we're looking at the physical controls it's worth checking your MIDI cables to see if any are causing any hum. After all, hum is another limiting factor when it comes to reducing background noise levels. Try unplugging and re‑inserting each relevant pair of MIDI cables; if you hear any change in background hum levels when you plug in a MIDI lead, you should replace it, as it is not correctly wired. Normally, hum level will go down as you unplug the offending cable, but if you have several that are mis‑wired, it may actually go up, and in this case you will have to carry on unplugging and replacing other MIDI cables until you cure the problem.
MIDI leads should have the screen of the cable connected to the centre pin of the 5‑pin DIN plug at each end of the cable, but the screen of the cable should not touch the metalwork of the plug itself (the body of the plug will normally be automatically connected to the metalwork of each MIDI device when it is plugged in, to provide extra screening). Particular cables to check are those game‑port adaptor cables that attach to PC soundcards to provide MIDI In/Out facilities — it's not unknown for these to be incorrectly wired.
Patching Up The Cracks
Figure 3: Most sequencers have options to treat MIDI velocity values after recording. Here is the Transform window in Logic Audio, showing a preset that ensures that no MIDI velocity will exceed 100.
Tweaking your synth patches to achieve maximum volume without distortion can also improve sound quality. Even in banks of commercial patches, some sounds play fairly quietly, or, worse, distort when several notes are played at high velocity. Even if you don't fancy creating your own sounds, it's normally comparatively easy to change the overall level of a patch (or each of its parts in proportion, in the case of a combination sound). If you're playing a melody or bassline using a single note you should find that if you increase the appropriate internal level parameter, the output level goes up, and you can pull down the mixer fader (along with the noise) significantly to compensate. With ambient or orchestral sounds this can make quite a difference, since you'll often be playing a single sound through each channel of your mixer.
Of course, you can also misuse internal MIDI levels as an effect. It's perfectly possible to take these level tweaks a bit too far, and end up internally clipping (overloading) the digital signals inside your MIDI synth. Since it's highly unlikely that you could do any damage, those of an industrial bent could generate overload and distortion effects by deliberately misusing MIDI in this way. However, since many modern synths have overload facilities built into their multi‑effects arsenal, this is probably only of use to the die‑hard experimenter in search of new sounds.
Whacking It Up
Once your synths and their sounds have been tweaked, there's a lot you can do within your sequencer package. If you're using half a dozen or less sounds from a module, increase MIDI Controller 7 (Volume) for each used channel from its default value of 100 to the maximum of 127. If you're running GM files, where every sound is coming from a single module, you'll probably need a value of 100 to prevent the overall levels overloading the synth output stage and causing distortion, but if you only use two or three sounds you can whack up the levels. If there is any other Master Volume setting available through MIDI control, make sure that this too is set to maximum.
Controller 7 can sometimes be accessed as Channel Volume on some synth editors, which makes for easier adjustment. If not, you'll need to insert an initial volume change at the very beginning of your sequence, since otherwise you may find the wrong initial volume when you restart your track, even if you're chasing controller values. This applies to any controllers used for level, pan, and so on, if they are altered during the course of the track.
After inserting a MIDI Volume = 127 command at the start of sequences, I measured a 5dB increase in output level from my Yamaha DB50XG. Since the mixer fader could then be lowered by the same amount, I had an effective improvement of 5dB in my signal‑to‑noise ratio for this synth.
Fading Away
Many people have found how useful MIDI Controller 11 (Expression) can be for real‑time volume automation using a sequencer, and very expressive results can be achieved. However, this technique may conspire against you where noise is concerned, since it involves lowering the synth level. If you're using MIDI volume automation for expression it's important to keep the overall level as high as possible — try to ensure that you're using the whole of the controller's range (see Figure 1).
If you're attempting to create fade‑ins and fade‑outs using MIDI Expression or Volume, remember that these are only 7‑bit controllers, with 128 volume steps. You may hear discrete steps in level rather than a smooth ramp at the low end of fades. If you have problems in this area, you can try to improve things by substituting volume control from any 14‑bit controller, such as pitch bend, which gives 16384 steps over the range.
Playing back just a single note on a module designed to output a dozen or more sounds may compromise noise level.
One thing to watch out for is that the MIDI All Notes Off command resets all Controller 11 (Expression) values back to their default 127. While this is handy when you're trying to keep noise levels low, if you automate a MIDI fade‑out you may get a sudden leap to full volume when pressing Stop on your sequencer.
By the way, don't worry about missing digital bits. In theory, synths that rely on digital mixing to alter volume levels may (depending on their design) be reducing in resolution as the level drops, and therefore using less digital bits. At very low MIDI controller levels your synths may sound more gritty, and just before the final fade disappears beneath the hiss, your sounds are left with a very buzzy quality. I've not had any problems with this on my gear, but it may vary from synth to synth. You can check it out by listening to a sequence with a very low MIDI controller 7 value, and with the speakers turned up.
However, although MIDI automation can produce very effective fades, there will always be noise left from the output stages of any synth, and this will be most obvious when the MIDI level is reduced to zero — you'll be left with a very messy tail‑end to your faded tracks. Performing fades on your mixer is the time‑honoured way to achieve best results, but automation is so much more elegant, satisfying and repeatable. For those of you using MIDI + Audio sequencers, a much better alternative when recording the final master is to record MIDI tracks onto a single stereo audio pair of tracks, and then use the audio fade options inside the sequencer, either with automated on‑screen faders, or by physically applying a fade to the digital data in your audio editor. The end of your fades will thus be wonderful digital silence, rather than musical silence set against the combined quiescent hiss from every synth in your setup.
The Final Perspective
Remember that the most obvious MIDI (and audio) noise is at the beginning and end of tracks. If you have a MIDI + Audio sequencer, by all means 'top and tail' the final audio recording to remove the worst of the background noise, but remember that you will still hear this same background noise during any quiet passages of the music, so it's well worth taking the effort to get this as low as possible before recording in the first place. Even if you use distorted sounds in your music they will probably sound better against a squeaky‑clean background.
It needn't take a lot of time to work through these tips — many things only need doing once for a lasting improvement. I must have increased the overall signal‑to‑noise ratios on my MIDI tracks by an estimated 10dB or so, and this level of improvement has to be well worth the effort.
Getting Keyed Up
Make sure you're using the whole of your keyboard's velocity range. Take a look in your sequencer at the highest and lowest recorded velocities of your performances. Some keyboards rarely get above MIDI velocity 100 unless you hit them with a hammer, and you may be missing out on the full range of expression from your sounds. Many sequencers allow you to transform or scale MIDI input velocities in real time as they are being recorded, and before they reach the destination synth via MIDI thru (see Figure 2). If your sequencer doesn't permit this, you may be able to find stand‑alone MIDI utilities that do it in real time before the MIDI data is passed on to the input of your sequencer.
Some master keyboards allow you to set up a different velocity response to adapt to your particular style of playing, to ensure that you're using the entire velocity range of 0 to 127. Also, some synth modules have different velocity curves available, and this can save you from having to reprogram a particularly unresponsive patch, although you'll probably find it easier to set up the keyboard if you have the option, since this will be a universal solution. People are sometimes surprised at the increased expression, even when playing commercial patches, after tweaking their keyboard response.
Don't forget that even if a given MIDI recording was played gently, with low resulting velocities, you can still scale this afterwards inside most sequencers — not only increasing MIDI velocity values, but also compressing and expanding them, to add more dynamics to the performance. You may have the opposite problem, in that a particular MIDI device distorts if you ever feed it a maximum velocity value of 127 (particularly when playing chords), because its patches were designed to suit a keyboard that never reached higher velocity values. To avoid any distortion during the performance itself, you could restrict the top values by limiting or scaling the value using a sequencer (see Figure 3).