Prepping for Your Mixing Session: Checking Your Monitoring

   By Lisa F   Categories: Audio SoftwareGeneralMixing Techniques

One of the most important things to attend to is your monitoring system – you have to be able to hear what you are doing properly when you are mixing. This means making sure that you are sitting in the ‘sweet spot’ at one of the three corners of an equilateral triangle with the left and right speakers positioned at the other corners facing you, and with the tweeters at about the same height as your ears.

You should make sure that the amplifiers have more than enough power to reproduce sound at the highest listening levels you intend to use without significant distortion and that the speakers have as ‘fl at’ a response as possible over as wide a range as possible. So-called ‘nearfield’ monitors (such as the previously-ubiquitous Yamaha NS10’s) that sit on stands, on desktops, or on the mixing console’s meter bridge can never reproduce the full range of the audio spectrum – because they have to be relatively small. This means that they will not be able to reproduce the bottom octave properly as their response will roll off significantly below, say, 80 or 100 Hz. This is why professional studios have large, full-range monitors – to make sure that the engineers and producers can hear all the frequencies correctly.

You also need to take into account the acoustics of the room that you are listening in. For example, consider the situation where you are trying to set the level of a bass drum correctly for your mix. The fundamental frequency of this instrument might be around 80 Hz or even lower. The length of the sound wave that is produced at this frequency (the wavelength corresponding to this frequency) would be somewhere around 4 metres, which could easily correspond to the width of the room that you are listening in. A ‘standing wave’ would very likely exist at this frequency, sitting between the walls of your listening room. If you are sitting at a point where the amplitude of this wave is zero or very low, the bass drum will sound too quiet, and you will almost certainly compensate by making this too loud in your mix. This is exactly what happens in my home studio, for example. Conversely, if you are sitting at a position within the standing wave where the amplitude of the wave is at a maximum, you will think that the bass drum is too loud – and you are likely to compensate for this by making the level of the bass drum too quiet in your mix.

Rooms can be designed or modified to minimize these effects and monitoring systems can be adjusted to compensate for the room acoustics. Professional studios off er properly designed rooms and monitoring systems – for hire at professional prices. Smaller project studios and home studios often overlook, or the owners cannot afford, such necessities. If your listening environment and equipment is compromised, particularly at the low frequencies, then you will have to listen on other systems that will reveal problems at the low end (or elsewhere in the frequency ranges, for that matter).

It is always a good idea to listen to your mixes on the kinds of speakers in the kinds of environments that will ultimately be used by your audience. So you might take your mixes out to a club, or play them in your car, or try them on your living room system – you get the idea. And don’t forget to check your mixes in mono – especially if you want them to sound right on radio, TV, or film where mono playback is still sometimes encountered.

A Note on External Mixing/Monitoring

It is possible to connect a Pro Tools|HD audio interface directly to your monitoring system, but this is not a good way to set your system up because the only way to conveniently control the volume of your monitors would be to lower the Master Fader (or the channel faders).

If you lower the levels in your mix just to make the sound in the room quieter, then you are almost inevitably going to be making the level of your mix too low if you then save this as a file, or route the mix to an external recorder, or whatever.

Also, although there may be volume controls on self-powered monitors or on the power amplifier that is driving your passive monitors, these controls are not normally going to be easy for you to reach while operating the system.

As most engineers will be aware, Pro Tools, like most DAWs, is designed to give best results when the Master Fader that controls the summed output level is kept around unity gain (the 0 dB fader position) while the channel faders set the levels of the individual mix elements in relation to this. Although Pro Tools does allow you to lower the Master Fader substantially without significant loss of resolution, it is not good working practice to do so. For example, if the converters are operating at very low levels, any non-linearity will be most pronounced at these levels.

One solution is to use some kind of external monitoring control unit that allows you to connect the outputs from your Pro Tools interface and provides a volume control that controls its outputs to your monitors. Such units may allow you to connect two or more sets of monitors and switch between these, and may provide additional talkback, dimming, or foldback/headphone facilities.

Another solution is to use some form of external mixer that incorporates these facilities. Using an external mixer provides another advantage: it allows you to completely avoid any latency due to your Pro Tools system while recording from external sources, because you can route these into the external mixer, monitor them directly from the mixer (with no latency delay), and route them in turn into Pro Tools to record.

Most professional mixers also incorporate a number of reasonably high quality microphone preamplifiers. These can be very useful if you are regularly recording from ‘live’ sources – and cost-effective compared with the price of buying lots of dedicated microphone preamplifiers.

Choose Your Monitoring Levels

There are no standard monitoring levels observed in music recording studios – unlike in film dubbing theatres, where the Society of Motion Picture and Television Engineers (SMPTE) has established a Sound Pressure Level (SPL) of 85 dB as a standard. This is normally referenced to an electrical signal level of −18 dBFS = 0 VU, which is the standard Operating Level recommended for digital systems by the Audio Engineering Society (AES). For the smaller rooms typically used for mixing music, a SPL of 83 dB may be more appropriate, with a nominal operating level of −20 dBFS providing 20 dB of headroom above this to accommodate signal peaks.

I have been at sessions in music studios that use monitoring levels well up into the 90s of decibels of SPL – or even more than 100 dB. Even relatively short exposure times to such high levels can make your ears ‘sing’ due to temporary threshold shift. Nevertheless, you may wish to check out the sound of some loud instruments that you have recorded at somewhere near to their original sound levels. And instruments such as the trumpet or snare drum can easily reach levels of over 100 dB, so it can be useful to have a monitoring system capable of reproducing such realistic levels.

Many engineers like to mix on small ‘nearfield’ monitors at quite low levels at somewhere between, say, 65 and 75 dB SPL. This makes it easier to tell whether the lead vocal or lead instrument can be heard properly at all times and whether other important elements such as the bass guitar and snare drum are at the right levels in relation to the lead. It also means that the mix should sound great when played back on domestic speakers after the record is released to the public. Of course, you can always check how it sounds from time to time at much louder volumes or on larger speakers.

Line-Up any Connected Analogue Equipment

If you connect your Pro Tools system to any analogue devices, such as mixers, tape recorders, or effects devices, you must make sure that the levels on the meters line up correctly. A 1 kHz test signal sent from Pro Tools at the chosen reference level, such as −20 dB relative to Full Scale, should produce a reading of 0 VU on an analogue VU meter connected to an analogue output from your Pro Tools interface. If it doesn’t match exactly, you will need to ‘tweak’ the calibration control on the VU meter until it does match – this is the procedure for ‘lining up’ meters.

To check that connected equipment is lined up correctly, you can insert the Signal Generator plug-in (see Figure 7.1) into one of the Master Fader Inserts, generate a 1 kHz sine wave test ‘tone’ at −20 dB, −18 dB, or whatever reference level is being used, and see whether the meters on connected equipment match this.

Figure 7.1: Using the Signal Generator plug-in to generate a test tone.

Recording a Test Tone to Disk

You can always record a test tone to disk, which can be useful if you will be transferring recordings to other systems, especially older analogue systems that need to be calibrated with their VU meters lined-up correctly.

To record a test tone to disk, simply insert the Signal Generator on an Auxiliary Input and bus its output to the input of an Audio track, as in Figure 7.2.

Figure 7.2: Recording a Test Tone at −20 dBFS to disk in mono from a Signal Generator plug-in inserted on an Auxiliary Input to an Audio track.

Creating a Test Tone Using AudioSuite

If you prefer, you can use the Signal Generator AudioSuite Plug-in to generate a 1-kHz sinewave at a suitable level to use as a reference tone so that other equipment can be aligned to in order to establish the correct value for 0 VU.

Make an empty Edit selection in an Audio track that lasts for 30 seconds, or however long you would like the test signal to last for, as in Figure 7.3.

Figure 7.3: An empty 30-second timeline selection.

Open the AudioSuite Signal Generator plug-in (see Figure 7.4) and choose the settings that you require.

Figure 7.4: Using the Signal Generator AudioSuite Plug-in to generate a test tone.

Typically, you will choose a sine wave tone with an appropriate peak level such as −18 or −20 dBFS here, then press Render to create a file on disk containing the test signal, as in Figure 7.5.

Figure 7.5: Thirty seconds of 1 kHz sine wave test tone.

You can supply this file along with your mixes – or record the audio from this in real time onto tape if you are transferring to tape.

Excerpt from Pro Tools 11: Music Production, Recording, Editing, and Mixing by Mike Collins © 2013 Taylor & Francis Group. All Rights Reserved.

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