Setting up a mixing desk input channel, The “channels tone controls”.
After you have set up the gain correctly, the next thing to move on to are the channels tone controls.
Use of mixing desk tone control.
Don’t try to do this before the main PA and monitor speaker systems have been set up. If you do you will be tying to compensate for the systems and rooms tone with a tool which is designed to sort out the individual channels; there associated mikes/ di boxes tone; the performers voice or instrument. Always use the system eq to sort the system and room out! Otherwise you will end up using all the channel eqs to sort the system and room out and all the channel eqs will end up wasted.
The tel tail is when you end up with all the channel’s eqs looking almost identical.
If your desk has a Hi pass filter turn it on if the channel is being used for a vocal or other non bass instrument, if the signal is a bass guitar or bass drum or music play back it off.
Basic two band tone control.
The use of the most basic two-band tone control is fairly crude. They comprise two shelving filters, a bass filter whose control will raise or lower the level of all frequencies in the signal below the bass filters cut of frequency and a treble filter whose control will raise or lower the level of all frequencies in the signal above the treble filters cut of frequency. If you have a system, which only has these, all you can do is boost or cut the treble or bass or if you cut both treble and bass together you can effectively boost the frequencies between the bass and treble controls frequencies. Conversely you can boost both treble and bass and effectively cut the frequencies between the bass and treble controls frequencies.
Procedure for setting up two band tone controls.
- up the gain as explained previously.
- Ensure all tone level controls are set flat i.e. in the 0 dB “12 o’clock” position.
- Apply the signal to the channel continuously.
· With the desks master fader set to its normal operating position of “0” dB (Nearly full up) gently raise the channel fader until the signal can be heard at a comfortable level. With one hand on the channel fader so the channel output can be swiftly reduced if feedback starts, use the other hand to increase the bass control, listening carefully to the resulting change in sound. Then reduce the bass control setting and again listen to the effect. Determine whether increasing or decreasing the setting of the bass control has a helpful effect, air on the side of “if it makes the sound less muffled or it stops the sound from being thin it is a good thing”, naturalness is a good starting point. Adjust the control to provide the optimum improvement in clarity. In some cases leaving it set at “0” is the correct thing to do.
· Again with one hand on the channel fader, use the other hand to increase the treble control, listening carefully to the resulting change in sound. Then reduce the treble control setting and again listen to the effect. Determine whether increasing or decreasing the setting of the treble control has a helpful effect, as with the bass control air on the side of “if it makes the sound less muffled or it stops the sound from being thin it is a good thing”, naturalness is a good starting point. Adjust the control to provide the optimum improvement in clarity. In some cases leaving it set at “0” is the correct thing to do.
· After the tone controls have been set check the level on the pfl meter as changing the tone control settings can result in the need to re set the gain.
Note It is often helpful to turn each tone control fully up and then fully down in turn with the other set to “0”to help your brain to get a feeling for what each tone control does, as no two desks tone controls are the same.
Simple three band tone controls
These are very similar to two band tone controls except the third filter the mid range is a band pass filter, in other words it controls frequencies that lie between its low frequency cut of and its high frequency cut off.
Procedure for setting up three band tone controls.
This is the same as for two band tone controls but you have to repeat the procedure for the mid range control. Mid tone controls can sometimes be helpful in removing feedback.
Swept mid frequency control
The addition of a frequency sweep to a mid range tone control is extremely useful. When you look at a desk for the first time it is essential that you determine what type of tone controls it has because using a swept mid in the same way you would use a high mid and low mid fixed frequency filter is hopeless and misleading. With a swept tone control there will be at least two control knobs associated with each frequency band, these will be labelled: –
Frequency or sweep, which controls the frequency that the pair of controls are going to effect. Note the legend around this control knob will indicate frequency in Hz or kHz
Level, which controls whether the frequency chosen by the frequency control is going to be boosted or cut in level and by how much. Note the legend around this control knob will indicate the amount of boost clockwise past 12 0’clock or cut anti clockwise from 12 O’clock
The main use of swept tone controls is to select a frequency that is causing trouble and reduce its level so it is in balance with the rest of the spectrum. This type of tone control should be likened to a sharp knife to be used to remove or adjust narrow band problems.
Procedure for setting up swept tone controls.
· Set up the gain as explained above.
· Ensure all tone level controls are set flat i.e. in the 0 dB “12 o’clock” position.
· Apply the signal to the channel continuously.
· With the desks master fader set to its normal operating position of “0” dB (Nearly full up) gently raise the channel fader until the signal can be heard at a comfortable level. . Listen to the sound and try to decide if there is anything that is clouding the sound or if there is something making the sound unnatural. Return the channel fader to its off position. Now set the mid range level control of the filter you are adjusting to maximum i.e. fully clockwise, this makes the frequency that the “ frequency knob” is pointing at more obvious when the channel fader is brought up again. Gently raise the channel fader again until the signal can be heard at a comfortable level.
· With one hand on the channel fader so the channel output can be swiftly reduced if feedback starts, use the other hand to slowly sweep the mid frequency control from its lowest frequency to its highest frequency, listening carefully to the resulting change in sound .It is likely that at some frequency in the sweep there will be a sudden increase in sound level, determine at which frequency this is worst and set the frequency control to this frequency, now reduce the level control of the filter to 0 dB i.e. 12 O’clock and then reduce it further until the problem frequency has been reduced so that it is in keeping with the rest of the spectrum. Check the setting of the filters level control by raising it and asking yourselves have I now got too much of this frequency, if you don’t try raisin it a bit more, if you do return it to its original setting Basically what you are trying to do is find the nasty bits and remove them.
· Repeat the procedure for all the swept tone controls in turn.
· After the tone controls have been set check the level on the pfl meter as changing the tone control settings can result in the need to re set the gain.
I hope this guide helps I will be posting further articles to cover other procedures I have come to trust.
