MIDI Muting is becoming more and more common as a standard feature on today's studio mixing consoles, and as well as performing routine mixing tasks, it has creative applications you may not have imagined. Paul White explains how MIDI muting works and how you can make best use of it.

Many of today's budget mixers come with MIDI muting fitted as standard, though if you haven't used a MIDI muting system before, you may not be aware of exactly what it can do for you and how best to use it. The vast majority of such systems are designed to be used in conjunction with an external MIDI sequencer which, in turn, means that the ease of editing is determined by the note editing capability of the sequencer you're using rather than by the mixing console itself.

The hardware for MIDI muting is relatively simple to understand — the conventional mute buttons on a console are replaced by non-latching buttons which serve to signal the internal microprocessor of your intent to mute or unmute a particular channel. The microprocessor then sends out a control signal, which activates an electronic switch, which turns off the channel output. If that was all that happened, then there would be no advantage over using conventional switches, but the fact that an internal microprocessor is involved means that MIDI messages can be sent whenever a mute switch is pressed. These messages can be stored in any MIDI sequencer (as far as the sequencer is concerned, it's just another musical performance), and when replayed into the desk, the microprocessor reads the MIDI data, and switches the channel mutes on and off automatically, exactly as you did when you recorded the data.

If all the music you're mixing is generated by sequenced instruments, then it really is as simple as that, but if you have a multitrack tape machine running into the mixer, you'll need to synchronise the sequencer to the tape machine using SMPTE or Smart FSK to ensure the timing is consistent and repeatable.

The beauty of using an external sequencer to record the MIDI data is that it can be edited in exactly the same way as you edit your music. Incorrect mutes can be deleted, new ones can be added and poor timing can be remedied by moving the mute data forwards or backwards in time. You can even go through a mix several times, recording the mute information a bit at a time to several sequencer tracks. Overdubbing the mute information in this way means you only have to worry about a few mute buttons each time you run through the mix, and when you've finally got all the parts right, you can merge the separate tracks to save space on your sequencer.

SNAPSHOTS

The majority of MIDI Mute systems also allow you to work in what is known as Snapshot mode. Essentially, a Snapshot (sometimes also called a Scene) is the mute status of the entire desk at one instant in time, and for most mixes, switching between a relatively small number of snapshots will be quite adequate. The advantage of working with Snapshots is that you can take your time setting each one up, then all you have to do is decide where you want the Snapshots to change. Snapshots can be called up directly using MIDI Program changes so you can treat them just like synth or effects unit patches, or on some systems, you can step through them manually using a button on the mixer or even a footswitch. This latter approach is useful if you don't have a sequencer. A typical use of Snapshots might be:

• Mute all the mixer channels until a fraction of a second before the first note of the song.

• The next snapshot might mute only the vocals and lead guitar solo.

• The next one switches on the vocal track just before the singing starts. When the guitar solo is imminent, the vocal track might be muted to kill any breathing noises or shuffling lyric sheets and the lead guitar track would be opened, just in time for the first note of the solo.

Ideally, all unused tracks should be muted to keep background noise and hiss to a bare minimum, but even if you don't take muting to extremes, the improvement in background noise can be quite dramatic.

HARD AND SOFT MUTING

At its simplest, MIDI muting takes the form of an electronic switch or even an electro-mechanical relay, but there are potential problems of which you should be aware. Though such switches may operate quite silently in the absence of any signal, any kind of fast switching that occurs during a signal is bound to cause an audible click or glitch. This is no fault of the system; it's simply a fact of physics that suddenly turning an electrical waveform on or off causes an audible discontinuity which we perceive as a click.

One way around this is to use so-called 'soft' muting. Instead of switching the audio on and off in an instant, soft switches fade the audio level up and down over a period of one tenth of a second or so, thereby avoiding clicks. Soft switching is obviously a desirable feature of any muting system, but because the mutes do take a finite, albeit very short, time to turn on or off, you should try to position your mute events slightly early (by a sixteenth of a bar or so if possible) to avoid the start or end of your wanted section being audibly affected by the fade time.

SUMMARY

MIDI Muting is no longer a luxury, and if you don't have a desk with MIDI Muting fitted, there are inexpensive third-party units that can be patched into your existing desk via the channel insert points. Modern recording equipment is now so good that the limiting factor in recorded sound quality is often the source material rather than the mixer or tape machine, so it makes sense to mute unwanted noise wherever possible. For example, guitar amplifiers generate hiss and hum, electronic synthesizers often throw out more electronic noise than we'd like, and budget effects units, while they may sound wonderful, are invariably noisier than their professional counterparts. By exercising a little care while recording and using a MIDI mute system at mixdown, even relatively modest equipment can produce master quality results.