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MIDI Muting

Sound Workshop


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.

Example of a MIDI Muting control section; this one's from the new Studiomaster P7 mixer.


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.

EDITING YOUR MIDI MUTE DATA

The MIDI data usually takes the form of MIDI note information where each mute button corresponds to a different MIDI note. Rather than use Note Ons to signify Mute Ons and Note Offs to signify Mute Offs, a more usual approach is to use note velocity information to determine whether the mute should be on or off. Typically, note velocities above the value of 64 might denote Mute Ons and velocities below 64 Mute Offs. Each Note On is immediately followed by a Note Off so that there is no need to record any long notes. This is important, because starting or stopping a mix part way through might otherwise lead to stuck notes, which would result in incorrect mute settings.

If a mix is started part way through, a basic system as described has no way of knowing what the mute settings should be — it can only respond to new MIDI information as it arrives. This means that the mute setting may well be wrong and will stay wrong until new mute data comes along to update the situation. One way of getting around this is to include extra MIDI data in the form of controller information, which encapsulates the mute setup of the entire console in one big burst of data. These bursts are recorded every second or so, which means that when you start a mix part way through, the mute status is corrected as soon as the next burst of controller information is received.

The new Studiomaster P7 console includes this system, though you do need a sequencer with the ability to selectively filter out controller information to get the best out of it. The reason for this is that, while note information is relatively easy to edit on a sequencer, controller information isn't. Therefore, if you perform extensive editing on your mute settings, the note information and controller information will disagree. For minor edits, this may not be a problem because the mixer only takes notice of the controller information for a few seconds to get itself set up, then it goes back to working on the MIDI note information. But if the editing is extensive, it may be wise to filter out the old controller information at the sequencer, play the sequenced note data back through the mixer and generate a new set of up-to-date controller information which may then be recorded on a new sequencer track.


CREATIVE APPLICATIONS: MUTING TRICKS

As pointed out earlier, if you can mute any mixer channels that are not in use, you'll end up with a much quieter, dearer sounding mix, but there are also one or two creative tricks you can do with MIDI Muting systems.

■ TIP 1
If you have MIDI Muting facilities on one or more of your aux sends, you can turn the feed to your effects units on and off, to add, for example, reverb or echo only to selected words, phrases or music lines. It also helps to mute the feed to your effects units up until the moment the song starts, as the effects of mix buss noise in a large desk can lead to relatively high levels of residual noise. If you don't have this facility, then consider feeding the effects units back through spare input channels rather than aux returns and mute these until the song gets under way.

■ TIP 2
Another incredibly useful option that is a real bonus for those working with few tape tracks is to feed the same tape track into two mixer channels using a splitter lead. By using the MIDI mutes to switch from one channel to the other, it is possible to set up two different levels, different EQ and pan settings and different effect send levels. If you've ever had to record a guitar solo onto a gap in the vocal track, you'll know how useful this could be. One channel could be set up for the vocals and the other for the guitar — all you have to do is switch before the guitar solo and switch back again before the singing starts again. Providing you have enough spare mixer channels, this trick can also be handy just for programming level changes where the two channels are set identically in all respects apart from the fader level.

■ TIP 3
Finally, you may have read in Recording Musician about using the side-chain input of a conventional gate to make one sound source chop up another in a rhythmic fashion. For example, if you were to play a sustained guitar chord through the gate and then externally trigger the gate using an eight-to-the-bar bass drum sound, you'd end up with eight bursts of guitar exactly in time with the bass drum. This kind of trick is very easy with a MIDI Mute system, as all you have to do is program the mute data for the channel in question to go on and off at the appropriate times. This is most easily achieved by entering the information directly into your sequencer, as trying to push a mute button up and down eight times per bar isn't really practical.

As an experiment, try placing eight evenly-spaced mute events in each bar and make each mute one sixteenth of a bar long. The sequencer's quantise function may be used to ensure the timing is spot on, and when you get more ambitious, you could try a more rhythmic sequence rather than sticking to straight fours or eights. In theory, soft muting systems are best for this job as they don't produce a click when gating in the middle of a sound, but in practice, because the result is percussive in nature, the click introduced by a hard muting system usually blends into the sound anyway.


More from these topics



Previous Article in this issue

Using Patchbays

Next article in this issue

Peavey PC1600


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Jun 1993

Topic:

MIDI

Mixing


Feature by Paul White

Previous article in this issue:

> Using Patchbays

Next article in this issue:

> Peavey PC1600


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