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Getting Started
- for Mixing Engineers |
Contents
Well, both really. Sound mixing, although in one sense a form of engineering, is also something of an art form, and can only be properly learned by a combination of technical understanding and working experience. It is not a simple subject, and any book covering the subject to a reasonable depth would be quite thick. These things said, one has to start somewhere and it is hoped that the information on this page will provide a useful starting point for sound engineers responsible for mixing, without getting too theoretical.
There are basically two aspects to sound mixing, which to some degree 'run in parallel'. The first aspect relates to the overall objectives − what you are aiming to achieve. The second aspect is the 'mechanics' of the operation − the practical tasks to be completed to get the system working so as to give the best quality of sound. It is very easy to go through the motions of a mixing technique whilst losing sight of the underlying objectives, so we will look at those first. Then we consider a possible mixing methodology.
For information about the facilities typically found on a mixer, see the Mixing Facilities page.
Each heading below states one of the fundamental objectives that you are aiming to achieve (not in any particular order), as far as practicable. In each case, some notes are provided (bulleted) related to that objective. In practice, you will find that these objectives are not independent of each other − indeed they all overlap to some extent. A little compromise on one is sometimes necessary in order to adequately satisfy another. These notes assume a relatively simple system, but the same basic principles can be extended to much larger systems.
Meet the Expectations of the Audience
- Remember − your job is not to create the kind of sound
that you would most like to hear! As with any art form,
tastes differ: everyone in the audience will have their
own idea of the perfect mix
and appropriate sound
level. Therefore, it
is impossible to totally please everybody all of the time − but
you can at least try to mostly please most of the people most of
the time, based on an appreciation of the nature of the
event.
- Don't forget the performers. There may be some tension between the interests of the performers and those of the audience (especially in smaller-sized venues), which the sound engineer must try to keep in balance.
Provide Appropriate Monitor Mixes at Appropriate Sound Levels
- Ensure that only the channels that the band really
need to hear are fed to each
monitor mix. Each of the
channels should be no louder in each mix than what the
respective band member (or members) really needs,
otherwise it will mask the sounds that they and other
performers are trying to hear and will tend to muddy
the overall sound heard by the audience.
- Check the monitor mix initially with headphones, and later (during sound-check or rehearsal) by listening to the monitor speakers.
Maintain an Appropriate Overall Sound Level
- The overall sound level needs to be appropriate to the location, occasion, and style of music. The appropriate level may vary throughout the course of the event. The overall sound heard by the audience is made up of the sound from the stage, plus the main ("front-of-house") PA sound, plus sound from the audience themselves. The sound from the stage is itself made up of direct vocal sound, plus direct instrument sound (including on-stage amplifiers, when used), plus the monitor sound. You have full control of the front-of-house sound level and some limited control of the sound level from the stage. Of course, you have no control of the audience-generated sound level but, in general, an audience will have no complaints about their own sound level!
- During the sound-check or rehearsal, take a walk around the room to check the sound level at different points, as it will be different at different points in the room. In general it will be louder nearer (and in line with) the speakers and nearer to the band, and quieter at the back where the mixer usually is, so if you feel it is too loud at the back it is fairly certain that those at the front will find it more so.
- During sound-check and rehearsal, remember that, depending on the size and acoustics of the space, it is probable that the sound level will be reduced somewhat by the presence of a large audience (due to absorption and consequent reduced reverberation), however there may be additional sound from audience participation and the band may play more enthusiastically once the audience has arrived!
- If the overall sound level is too low, you can generally increase the front-of-house level, subject to the limits of feedback (see below) and the maximum power ratings of your equipment. Be aware, though, that in smaller venues where the sound from the stage (direct sound e.g. from drums, backline sound and monitor sound) is significant in the mix heard by the audience, front-of-house level changes may affect the balance between the sound sources in the mix.
- If the overall sound level is too high, you need to consider why − in smaller venues the stage sound level may be making a significant contribution. In the sound-check or rehearsal, try simply shutting off the front-of-house speakers − if the sound level doesn't reduce quite significantly then either the monitors are too loud or the band itself (i.e. backline plus acoustic drum kit etc.) is too loud. It can sometimes be difficult for a loud band to understand that less on-stage sound can result in an a better quality of overall front-of-house sound and a more appreciative audience.
- Listen carefully. Can you hear each sound source making its proper contribution? (This does not mean that each sound should be at the same sound level.) Does anything stand out as being disproportionately loud? The balance may well be different at different points in the room, so check this during the sound-check or rehearsal. And of course the balance between the various sounds will often intentionally be varied by a band during a song, for the sake of variety. So keep listening carefully.
- Possible causes of poor sound clarity are inappropriate EQ settings, over-loud monitors, distortion (often caused by incorrectly set mixer gain controls) and inadequate, poor quality, or faulty equipment.
- Feedback (of the acoustic variety) occurs when the total amplification between one or more mics and the speakers (monitors, main, or both) exceeds a critical amount. To avoid it the amplification between the mic(s) and speaker(s) concerned must be kept below that amount.
- If reducing the amplification to avoid feedback results in too low a sound level, then ideally more output is required from the mic. This means that the mic needs to be nearer to the sound source (e.g. vocalist's mouth) or that the sound source itself (e.g. voice) needs to be louder. If neither of these solutions is practicable, then the amount of amplification that is achievable without feedback occurring can usually be increased a little by adjusting the EQ of the channel(s) involved in the feedback (not by adjusting the main graphic equaliser, which would affect all channels − though a monitor mix graphic equaliser can be useful here). The EQ will need to be changed to increase the cut (or reduce any existing boost) at the particular frequency where feedback would first occur, but take care to avoid any unacceptable reduction in clarity.
- For more detailed guidance on this subject, see How can I avoid feedback? on the FAQ page.
For those who are new to mixing, one of the main problems can be knowing where to start. The key is to adopt a methodical approach.
No two PA systems are identical − there always will be differences in aspects such as:
- The complexity of the PA equipment
- The size and acoustics of the venue
- The number of signal sources (microphones, instruments, etc.)
- The requirements of the performers
- Time constraints for set-up and sound-checks
- The expectations of the audience
- In-house or mobile system
Nevertheless, it is possible to generalise to a large degree as to how the task should be approached. The following is a tried and tested method which should be useful in the vast majority of situations. However, it is by no means the only approach, and others may work just as well. For convenience it is arranged into six major stages, each consisting of a number of steps. For example, in the case of a permanently installed in-house system with the speakers properly equalised, you can ignore stages 2 and 3.
- Stage 1 − Starting Point:
We are assuming the following
starting point − this is very important:
- The system has already been fully assembled (see the Assembling a System page).
- The signal sources have been assigned to the mixer channels and the mixer marked-up accordingly.
- All channel EQ set flat.
- Channel aux sends at 50% of travel, for the specific channels that are required in each monitor mix. All other channel aux sends at minimum.
- All channel faders at minimum.
- All pan controls centered.
- All group and main faders at their '0 dB' setting, if marked − otherwise at approx 65% of travel.
- All master aux sends at minimum.
- All graphic equaliser controls set flat ('0 dB' setting).
- All amplifier level controls at minimum.
- All equipment switched on, in the correct sequence:
- Performers' equipment
- then effects units, tape and CD players
- then the mixer
- then graphic equalisers
- and finally, the amplifiers.
- Stage 2a − Amplifier Levels
(single-amped system):
For a single-amped system (i.e. one in which
there are not separate amplifiers for each frequency range),
set the level control of each amplifier, one at a time, as follows:
- Play a suitable tape or CD into a spare channel. (The more similar the recorded programme material to the live programme material, the better.)
- Set the gain control of that channel using the mixer's metering facilities. For best results, do this using the method detailed in the mixer manufacturer's instructions.
- Route that channel to the required amplifer, using the appropriate pan control and/or group assign switches.
- Set the channel fader to its '0 dB' setting, if marked − otherwise to 65% of travel.
- Gradually advance the appropriate amplifier level control until the desired sound level from the associated speakers is obtained. (Of course, this assumes that the amplifiers and speakers are rated appropriately for the job.) Remember that any other speakers in the system (plus backline, plus audience sound) will eventually be making their own contribution to the final overall sound level in the venue.
- Stage 2b − Crossover Levels
(multi-amped system):
For a multi-amped system (one having separate
amplifiers for each frequency range), first set the
crossover frequencies
to suit the speakers, then proceed as for a single-amped
system above, but for each group of amplifiers set the level for each
frequency range as follows:
- Play an audio test CD, having a separate track for each frequency range used, into the spare channel. (N.B. Be sure that the channel EQ is set flat!)
- Using a sound level meter with weighting switched off (or, if that's not possible, set to C-weighting), set the level for each frequency range such that similar meter readings are obtained for each range. (Do not adjust the mixer settings during this process!)
- Finally set the overall level for that group of amplifiers by playing a normal programme CD, as for a single-amped system.
- Stage 3 − FOH Graphic:
Ideally, set the FOH
graphic equaliser as per the steps below. However,
if you don't have an audio test CD or a sound level meter, or the proper
method would take too long, then you must set it by ear using a programme CD
(as used in Stage 2a) − but this relies on you knowing exactly what the CD
should sound like.
- Play an audio test CD, having a separate track for each frequency band of the graphic, into the spare channel. (N.B. Be sure that the channel EQ is set flat!) Use a test CD with tracks of band-limited pink noise, not single-frequency tones.
- Initially re-adjust the gain control of that channel if necessary, but do not adjust it from track to track!
- Using a sound level meter with weighting switched off (or, if that's not possible, set to C-weighting), set the graphic equaliser slider for each frequency band such that similar meter readings are obtained for each band. For each band, take the average of readings made at several locations throughout the venue. (Do not adjust the mixer settings during this process!)
- Remember that the speaker system may not have a frequency range wide enough to handle the frequencies affected by the controls at the extreme upper and/or lower ends of the graphic equaliser frequency range. Do not attempt to equalise frequencies outside the range of the speaker system (or of the sound level meter); leave the controls for those bands set at the central (0 dB) position.
- Stage 4 − Channel Set-up: For each channel in turn:
- Arrange for the actual signal source for the channel to be continuously present (e.g. by getting the performer to perform continuously).
- Set the gain control using the mixer's metering facilities. For best results, do this using the method detailed in the manufacturer's instructions.
- Listen to the channel on the headphones using the PFL
facility, and make preliminary adjustments to the channel
EQ. Some simple guidance on using the EQ:
- Don't make unnecessary adjustments − if no EQ is needed then leave it set flat.
- Only adjust one control at a time (or one pair, if it's a sweep EQ control). Then listen for a while, and re-adjust that control if necessary.
- Start by making any necessary adjustments to the bass (control(s) marked 'Low' or 'Lo') and treble (control(s) marked 'High' or 'Hi'). Then move to the 'mid' frequencies.
- When the sound is close to what you require, only make small adjustments. Then listen for a while and make further small adjustments if necessary.
- If the mixer requires it, re-adjust the gain control (to compensate for any large changes in EQ).
- Assign the channel to the required group.
- Temporarily fade up the channel to listen to it on the FOH speakers, and fine-tune the channel EQ. (For this step, it is usually helpful to fade up the channel to a higher level than would be required for it in the final mix.) Then fade it fully down again.
- Stage 5 − Monitor Mixes:
When all the channels are set up as above,
arrange for the actual signal sources to be "continuously"
(as far as practicable) present on all channels simultaneously.
A full rehearsal is ideal for this (but the performers need to
understand that they will not be hearing any sound from the
FOH speakers yet). Then set the monitor mixes as follows:
- First roughly set the overall monitor levels by advancing each master aux send control until the required sound level is reached on each monitor. (The aux send controls of the specific channels that are required in each monitor mix were set to 50% in 'Starting Point'.)
- Then create the monitor mixes by varying the aux send controls from their 50% positions, to suit the requirements of the performers.
- If necessary, re-adjust the overall monitor levels. (Take care to avoid unnecessarily high sound levels on stage.)
- Stage 6 − FOH Mix:
Finally, set the FOH mix as follows:
- First set the overall FOH level by fading fully down the main fader, setting every channel fader to its '−5dB' setting, if marked − otherwise at approx 60% of travel, and then advancing the main fader until the required level is reached. (The group faders are still at '0 dB', or approx 65% of travel.)
- Then create the required FOH mix by varying the channel faders from their '−5 dB' positions.
- If any channel fader positions exeeed '+3 dB', or more than 20% of them exceed '−5 dB', then increase the main fader setting and back off all the channel faders by a corresponding amount. (This avoids overloading the summing amplifier of the desk.)
- If all channel fader positions are below '−15 dB' then decrease the main fader setting and increase all the channel faders by a corresponding amount. (This maintains a satisfactory signal-to-noise ratio from the summing amplifier of the desk.)
- If necessary, re-adjust the overall FOH level using the main fader.
This page last updated 09-Sep-2011.