Compress | • Ratio: This determines the change in output level as a |
| function of the change in input level, once the |
| threshold has been exceeded. It is calibrated in |
| decibels, with a range from 1:1 (off) to 20:1. Thus, if it |
| is set to 10:1, an increase in input level of 10 dB |
| (assuming the input is above the threshold level), |
| results in a 1 dB increase in output level. |
| As a general rule, use ratio settings from 1:1.5 to 1:5 |
| for compressor use. Settings from 1:10 to 1:20 are |
| more useful for limiting purposes, because in that |
| range the output level changes very little as the input |
| increases. |
| • Output: This determines the overall gain of the |
| compressor from input to output (as measured with |
| the signal below the threshold level). You can use this |
| control to compensate for the loss of gain caused by |
| the action of the compressor. It is calibrated in |
| decibels, with a range from unity (0 dB) to +20.0 dB. |
| Automix |
Click this button to open the Compressor window for the A and B outputs. Each compressor has five knobs: Attack, Release, Threshold, Ratio, and Output. Click and drag on the individual knobs to adjust each parameter. An
Click the ON button to turn each Compressor on and off. The Compressor can also be turned on and off with the buttons on the output strip. Click the RESET button to return all the knobs to their default settings.
The A to B button (and corresponding B to A button on the B side) copy the settings of the A Compressor to the B Compressor (and vice versa).
About Compression:
A compressor is used to reduce or limit transient peaks in a signal. As the input level to the compressor increases, the output level increases linearly until the threshold point is reached. After that point, the output level no longer increases linearly, but increases at a reduced rate that is determined by the ratio setting.
•Threshold: This control determines the level at which the compressor begins to act on the incoming signal. It is calibrated in decibels, with a range from
•Attack: This determines how fast the compressor reacts once the threshold has been exceeded. It is calibrated in milliseconds, with a range from 1 ms to 2500 ms (2.5 seconds).
•Release: This determines how fast the compressor turns off once the signal falls below the threshold. It is calibrated in milliseconds, with a range from 10 ms to 2500 ms (2.5 seconds).
One of the dangers of using a conventional mixer in a sound system operated by an untrained sound technician is the occurrence of feedback. The more open channels there are, the greater the overall system gain and the lower the potential acoustic gain (gain before feedback).
A trained operator knows that when a single microphone is on, the gain of the single channel can be turned up to a point just before feedback starts to occur, and then backed off a little to provide a safety margin (feedback stability margin). But if a second microphone is turned on, the first microphone’s gain must be reduced to compensate for the additional gain provided by the second microphone. If the first microphone isn’t turned down, feedback could occur.
The Automix feature automatically adjusts the
input gains, depending on how many open channels there are at any given time. This number of open microphones (NOM) is used to calculate the gain adjustment (attenuation) for each channel.
24– DX8