Analogue Mixers

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The purpose of an analogue mixer is simple - to bring several sound sources together into one central location and then manipulate and feed the signals to the relevant locations. This concept holds true from the smallest 'notepad' mixer through to large consoles costing hundreds of thousands of dollars. Most desks offer a standard set of connections and perform a number of core functions - once you understand these concepts you should be able to comfortably operate almost any analogue mixer.

We'll start off looking at the channel section - a desk will have a number of channels, commonly from 8 through to 32 or higher. Each channel is discrete from the others but will have the same controls. Once you understand one channel you will understand them all!

Channel Inputs

These are the sockets that allow you to feed audio into your mixer. The usual inputs are a 1/4 inch socket that accepts line-level signals (i.e. CD Players, Synths) and a XLR socket which is used for 'mic-level' signals such as microphones and DI Boxes. Nearly all desks offer 'Phantom Power', sometimes denoted as '+48v'. This is the required power supply to run capacitor/condenser microphones. Cheaper desks may have a global phantom-power button, sending +48v to all mic inputs when depressed. Better desks have switchable phantom-power on each channel.

Most budget desks will only allow the channel to 'see' one input at a time, usually with a mic/line switch, although more expensive studio desks will allow you to use both inputs simultaneously, effectively doubling the number of channels available.

Most channels are mono although many modern desks will offer a few stereo channels - this are often fed via 1/4 inchs and/or RCA Phono.

If the desk does not have a dedicated FX/Aux return section then hardware FX units will be connected to channel input, often stereo, via the line input.

Channel Insert

The Insert socket on a desk, normally a 1/4 inch socket, is actually a send and return point on a single stereo jack. This means audio is carried in 2 directions, in and out of the desk, on one cable. The insert point is used to feed 'processors' (compressors, gates, hardware EQ etc) and bring the processed signal back into the desk. An insert point will often terminate into a patchbay to allow more convenient patching of processors and to save wear and tear on the desks insert socket. Insert points are sometimes switchable between pre or post fader meaning that the signal level going to the insert point is not controlled by the fader (pre fader) or is dependent on the fader position (post fader).

Gain Control

The gain control allows you to amplify or attenuate the signal coming into the desk. This is often used in conjunction with the 'PFL' button (mentioned later). Gain structure is important to ensure the optimal signal to noise ratio and to prevent clipping/distortion of the signal. Mic level inputs will usually require more gain than line level inputs. Gain is usually set so that the average level of the signal is at 0dB on the level meters.

High Pass Filter

The HPF switch, sometimes called a LCF or similar, applies a filter to remove all frequencies below a set cutoff. This cutoff varies from desk to desk but is often around 80-100Hz. This can help remove low frequency noise such as mechanical vibrations through a mic stand or plosives from a vocal recording.

Phase Reverse

This control inverts the polarity of the signal. This is useful when signals are suffering from phase related problems. A common use for this is to invert the phase of a mic underneath the snare drum if there is another mic above the snare drum being recorded.

EQ Section

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The EQ section is where the sound is sculpted tonally. Most desks offer between 2 and 4 bands of EQ, usually a LF (low frequency) and HF (high frequency) control and 1 or 2 controls for the MF (mid frequencies). Each band will have a cut/boost control, essentially a gain control, calibrated in dB which allows you to amplify or attenuate. The MF band(s) will usually have a sweepable frequency control which allows you to decide where you want to amplify or attenuate the signal. Some desks offer this control on the LF and HF bands also, but more often than not they are 'shelves' with a fixed cutoff point. Desks with 'parametric' EQ sections will also offer a 'Q' control. This decides how wide or narrow the boost is (the bandwidth) with the centre being determined by the freq control.

Auxiliary Sends

The aux section is the point in the signal path where the signal is sent off to other locations, either for manipulation by effects units (reverb, delay, chorus, flange) or for monitoring purposes (headphones for musicians, on stage monitors for performers) A desk will usually have between 2 and 8 aux sends.

Like the insert point, aux sends are switchable or pre-configured as either pre or post fader. Pre fader aux sends are used for monitoring purposes, and occasionally certain special effects. Post fader aux sends are used for feeding effects units.

Unlike the insert point, the aux section allows you control over how much signal is sent to its location. Also the aux is a one way connection unlike the insert point. This means that the effected signal doesn't come back into the channel like a processed signal - instead the effected signals will come back elsewhere on the desk, preferably into an aux return section, or failing that a normal channel.

Pan/Balance Control

The pan (short for panorama) control allows you to position the sound anywhere you like in the stereo soundscape. With the control fully to the left, the signal will be sent to the left speaker only, with the control in the centre the signal will be split equally between the 2 speakers, and with the control fully to the right it will be sent to the right speaker only. Pan controls are found on mono channels only. Stereo channels have a balance control instead which is allows you to 'balance' the stereo signals left and right levels rather than positioning the signal like a pan control. The pan control can also be used to route signals to specific groups on desks with group outputs.

Fader

The faders job is quite simple - it allows you to alter the level of the signal leaving the channel. When the fader is set at 0dB the signal will be at the same level as when the gain is set in conjunction with the PFL control.

PFL

PFL stands for Pre Fade Listen and allows you to isolate one channel or more and hear it in isolation pre fader. This is useful for setting the gain as the meters on the desk will only show the levels of the channel(s) which have the PFL button depressed. PFL will allow you to hear any changes made to the signal with the EQ section but not changes made with aux sends or pan. PFL produces a mono signal on mono channels and a stereo signal on stereo channels.

AFL

AFL stands for After Fade Listen and allows to isolate one channel or more and hear it in isolation post fader. This function is useful for monitoring the signal being sent from aux sends to FX units or headphones/stage monitors. AFL is mono on mono channels and stereo on stereo channels.

Solo

The solo control allows you to isolate one channel or more and hear it in isolation post fader and post pan/balance. Therefore this signal is stereo regardless of the input.

Routing Controls

These controls allow where to send the signal post fader. The most common location is L-R which is the main faders (Left and Right). However there are often group options available. Groups allow you to control several signals with fewer faders. For instance a drum kit that uses 8 channels could be sent to a stereo group and be controlled overall by 2 faders. The number of groups a desk offers can vary between 2 and 8.

Groups can also be used for other purposes, most commonly sending signals to a recording device. Group buttons are usually labeled with 2 consecutive numbers corresponding to the groups such as 1-2, 3-4, 5-6, 7-8 etc. If you send channel 1, panned centrally, to groups 1 and 2 the signal will be equal in both groups. If you pan the signal left it will only appear in group 1, and if you pan the signal right it will only appear in group 2. Odd numbers are always accessed by panning left and even numbers by panning right.

Smaller desks may not have groups, but may instead have a stereo 'submix' option which is essentially the same as 2 groups.

Group Faders

As the name suggests this is a bank of faders which control the levels of the groups. The groups themselves can be routed to L-R so they are audible, or in some circumstances, such as being used to feed a recorder via Grp outputs, they can be inaudible by not routing them to L-R.

Tape Return Section

This section is only available on more expensive studio desks so you may not come across this too often on budget desks. There is usually one tape return for every channel on the desk. The section itself is found within the normal channel section on 'in-line' desks, or in a dedicated tape return section to the right of the L-R faders in 'split' consoles. The tape return section is essentially a mini channel with EQ, Pan and level controls that allows you to monitor what has been recorded or is being recorded onto tape. When we talk about tape in this context, we are actually talking about whatever medium you are recording onto whether it be analogue tape, hard drive, ADAT etc.

Tape In

This is the socket to which your recording device outputs are connected to if your desk has a tape return section (see above) These are often 1/4 inch and mono.

2 Trk Input

The 2 Trk input is commonly used to connect a CD player or other stereo playback device. Stereo mastering devices such as DAT machines are also often connected via this input.

Dir/Grp Outputs

This is the most common way to get audio from the desk to a multitrack recorder. Most medium sized analogue desks have direct outputs for each mono channel, and some will also have group outputs for each mono channel although they are usually both accessed from the same physical output (often 1/4 inch) and switchable.

Direct outputs are hardwired to the relevant channel so that channel 1 on the desk will go to input 1 on the recorder, channel 2 to input 2 and so on. Group outputs allow more flexibility in the routing and allow any channel to be sent to any input on the recorder. This is determined by the routing and panning of a signal in a channel as mentioned earlier.

FX/Aux Return Section

This is a feature found on more expensive desks and allows FX units to be returned to their own dedicated channels rather than having to use normal audio channels which could be used for normal audio inputs. The FX return section is like a mini channel with gain, basic EQ, pan, level and routing controls.

Ctrl Room Out

These outputs are fed by the master L-R faders, via the Ctrl Room Level, and are connected to your amplifier/active monitors.

Ctrl Room Level

This is a volume control for your speakers and should be used rather than the L-R faders to control the volume in the control room.

L-R/Master Fader

These are the faders (although some manufacturers only use one) that control the overall level of all signals routed to the L-R buss. In studio situations they are often left around the 0dB mark.

Master Inserts

These are identical in operation to channel inserts but take the signal from L-R. For this reason they are used for mastering processors such as compressors, exciters and limiters which effect the entire mix.

Master Out

These sockets will typically feed your mastering device. This could be a hardware CD burner, a DAT machine or a pair of inputs on an audio interface. The signal level is determined by the position of the L-R faders.