The recording studio - Mixer: channels

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Via the channels, the signal is picked up, manipulated and sent to the appropriate destinations. In actual fact, every one of the mixer's channels contains two channels, but for the moment let's pretend there is only one and concentrate on this single channel only.

The recording studio - Diagram of a mixer's channel

Diagram of a mixer's channel

A channel can receive both a line input and a balanced microphone input [Balanced electric connections ] . The main difference between these two signals is that a microphone signal has a far lower voltage than a line signal[12 ], and therefore the two inputs are amplified differently (for a more detailed explanation of this topic, go to the amplification section [Amplification ] ).

Let's take a look at the various stages of a channel:

  • Gain:

    The recording studio - Gain


    Both inputs, the line input and the microphone input, have a gain potentiometer which regulates the signal's amplification level; often it is the same potentiometer that controls the two gain circuits. Through a switch we'd then select the kind of input (microphone or line).

  • PAD (attenuation): allows input signals that are too high to be decreased by 20-30 dB.

  • Phase inverter: from this stage onwards the channel becomes a single channel. This stage literally inverts the phase (swaps the negative pole with the positive pole).

  • Equalizer: parametric equalizer. For a detailed description go to the pertaining section [Parametric equalizers ] .

    The recording studio - Parametric equalizer

    Parametric equalizer

  • Filter: supplies the channel with a high-pass filter [Filters ] which makes sure low frequencies are efficiently removed.

    The recording studio - Filter


  • Insert socket: this socket is actually located in the posterior connections of the mixer, not on the channel strip itself. We have access to this socket via the patchbay [PatchBay ] which shall be described later. It consists in two sockets through which one or more effects can be insert in series, as shown in the following diagram:

    The recording studio - Insert socket

    Insert socket

    By inserting a connector into the insert-out socket, the direct insert-out/insert-in connection is broken and the signal is sent through the external modules.

  • Auxiliary send:

    The recording studio - Auxiliary send

    Auxiliary send

    These are potentiometers that pick up a copy of the channel's signal and send it to an appropriate bus[13 ]. To gain a better understanding of the way aux send works, we will refer to the following diagram:

    The recording studio - Example of aux send

    Example of aux send

    In our example we have imagined 4 aux send potentiometers for each channel, two pre-faders and two post-faders. This means that the copy of the signal that is picked up by an aux send pre-fader is independent from the channel's main fader, whereas the one picked up by the post-fader isn't. Later on we will see when one type of aux send is needed rather than another.

    Through aux sends we can create a series of auxiliary mixes whose overall levels are controlled by their respective aux send master (that are located in another section of the mixer and which we will investigate later [Aux send master ] ). For the time being let's not get too bogged down in aux sends which will be fully described in due course.

  • Routing matrix: its function is to route the signal towards the groups (group buses are located in another section of the mixer which we'll be looking at shortly [Mixer: groups ] ) or towards the stereo bus L-R [Master fader ] . If our mixer were to have 8 groups, we could route the signal to any group couple and also to the mix bus through the routing matrix (in our mixer's case: 1-2, 3-4, 5-6, 7-8, L-R).

    The recording studio - Routing matrix

    Routing matrix

  • Mute: by pressing this button, the channel is muted. There are various situations in which this is necessary (for example, imagine that during mixing you wanted to listen to the recording without vocals, in this case all you'd have to do is press the mute button on the vocal channel, rather than turn the fader down manually, and moreover losing its original position).

    The recording studio - Mute button

    Mute button

  • Solo: by pressing this button all the other channels are put in mute mode (imagining, for example, that we only wanted to hear the voice this time, if we press the solo button on the vocal channel, all the other channels would thereby be muted).

    The recording studio - Solo button

    Solo button

  • Fader: it controls the amount of signal routed to the mix bus or to the groups. In the following diagram we can distinguish the signal-routing buttons that route the signal towards the groups or towards the mix-bus.

    The recording studio - Fader


  • Panpot (panoramic potentiometer): controls the percentage of the signal sent to a bus couple. If, for example, the panoramic control is rotated entirely clock wise and the routing matrix sends the signal to the group-couple 7-8, the channel's signal would be routed towards bus 8. If, on the other hand, the pan is rotated entirely anti-clock wise, the signal will be routed to bus 7. With the panoramic control in a central position, the signal will be equally distributed to bus 7 and 8.

    The recording studio - Panpot


  • Monitor fader: in the recording studio, signals are recorded at levels suitable for recording and therefore it is crucial to be able to separate the recording levels from the listening ones. This is why in actual fact a studio mixer has two channels within each single channel strip.

    The second channel, called monitor path and located underneath the main channel, serves the purpose of feeding the so-called monitor bus. For the moment it will suffice to know that on each channel there is another fader, which is usually smaller than the main one, which routes the signal towards this new bus.

    The recording studio - Monitor fader

    Monitor fader

    Every monitor path's fader works in combination with its respective panoramic potentiometer. The latter controls the percentage of signal picked up at the channel-input to be sent to the left and right sides of the monitor bus.

    We will call the channel that passes through the larger fader main channel and the one we've just described monitor channel. The reason why there are two channels in one, is that a mixer can undertake two status': the recording status and the mixing status. We can guess by their names what their functions are. What is important however, is that depending on the status of the mixer, the main channel and the monitor channel are fed by different signals and thus have different functions. We will see this in greater detail further on, when we will describe the recording and mixing phases.

[12 ] the input lines are used with signals coming from preamplified circuits. In other words, the line signals have already gone through its preamplfication stage and therefore have a higher voltage. Another difference concerns impedance adaptation, which is explained in its pertaining section [Direct Injection Box aka DI box ] .

[13 ] A bus is a channel in which a series of signals are made to converge. The mixer's most important bus is the output stereo bus, from which the resulting signal of the channel's mixing is picked up. Other buses include group buses, solo buses and monitor buses, which will all be described in the next section.


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