In the last part of our series we explained the basics for recording guitars. Now it is about the sound processing and improvement of the recorded audio track. To this time, one of the most important audio processing tools is presented: the compressor. It might not be very easy to understand in the beginning, but with a little practice you will become more familiar in dealing with it.
In the following I will show which settings are possible for a compressor and what they do by using a plug-in for the Software ProTools. These parameters are almost identical for all compressors, so it does not matter which compressor is used for guitar recording.
The compressor simply makes it sound loud and soft in an audio track. It thus restricts the dynamic capture of an audio track. As a result, the overall volume of the audio track can be increased without distortion.
At first, an uncompressed guitar track:
In order for the compressor to work properly, some parameters must be set.
The Threshold controls the volume at which the compressor begins to operate. In order to understand the threshold, it is first necessary to know that the level of an audio signal is measured in decibels (dB). At 0 dB, the maximum possible level at which the audio signal is reproduced is distortion-free. All levels below this maximum level are given with negative decibels. For example, if the maximum volume of an audio track is -4 dB and the threshold is set to 0 dB, the compressor will not engage. This is due to the fact that -4 dB is quieter than the set 0 dB and thus no level peaks can be made quieter. In order for the compressor to work, the value of the threshold must be less than the maximum volume of the audio track, in this example of -18 dB. The compressor thus engages at all decibels which are greater than -18 dB.
The ratio indicates the extent as to which the compressor intervenes when the threshold is exceeded. For example, a ratio of 2: 1 causes the level crossing the threshold to be halved. If the threshold is set to -6 dB and the audio track exceeds the threshold by 4 dB, the signal is halved and the 4 dB is divided by 2. The overshoot is thus reduced from 4 dB to 2 dB, the audio track consequently quieter. A ratio of 4: 1 would accordingly give a reduction to 1 dB, a ratio of 8: 1 a reduction to 0.5 dB and so on. You can hear the different effects this produces in the following sound examples:
Example sound at Threshold -18 dB and Ratio 2: 1
Example sound at Threshold -18 dB and Ratio 4: 1
The signal has become quieter due to the volume control of the level peaks. This makes it possible to increase the gain, ie the overall volume, of the entire audio track, without distortions.
Example sound at gain increase of 6 dB, audio track NOT compressed
Example sound at gain increase of 6 dB, ratio 4: 1 and compressed
Attack / Release:
The Attack parameter determines how quickly the compressor is to be interrupted after the threshold is exceeded. The Release parameter controls when the compression rate should reach the value 1: 1 again. In the following two extreme examples, so that one can perceive the differences in the settings well:
Example sound at attack / release stop left
Example sound at attack / release stop right
Finally, it should be noted that, with all knowledge about the various parameters, the hearing should have a decisive influence during guitar recording!