How to Master Your Finished Audio Recording Part 3:
Common Recording Problems that a Compressor Can Fix
Here are several common problems you can run into when using a compressor and how to fix them:
| Problem: |
Explanation: |
| Breathing |
If the audio material has a wide dynamic range, the output gain of a compressor can vary greatly. The greatest change occurs immediately after the input signal crosses the threshold. If the input signal fluctuates around the threshold, then the output level will increase and decrease repeatedly. The resulting rise and fall of low-level background noise can result in an annoying “breathing” effect. To prevent this effect, use a lower compression ratio, or increase the release time. |
| Pumping |
Pumping can occur when you compress a mix where one instrument is louder than all others. Whenever the loudest instrument is silent, even for a brief moment, the overall level of the other instruments will increase dramatically. As the dominant instrument comes in and out of the mix, the compressor will increase and then reduce the level of the other instruments. This results in an undesirable “pumping” effect. To prevent this effect, decrease the level and/or dynamic range of the dominant instrument in the mix, increase the threshold, or use a lower compression ratio. |
| Noise |
Set the gate so that the noise floor is not boosted significantly during quiet passages. |
| Harmonic Distortion |
If the release time is too short when compressing or limiting low-frequency signals (such as a bass guitar), the compressor or limiter can respond to the actual individual cycles of the waveform, causing harmonic distortion. To prevent this effect, increase the release time. |
Studio Recording Effects: Compressor / Limiter:
The purpose of the limiter is to prevent the audio signal from exceeding a threshold value. The most common problem caused by the use of a limiter is excessive distortion. This indicates that the limiter is active too much of the time, or that the master gain is set too high. To correct the distortion, lower the master gain or increase the threshold. A limiter may be thought of as an extreme case of compressing. Its parameters include the following:
| Setting: |
Range of Values: |
| Compressor Threshold |
From -40dB to 0dB |
| Master Gain |
From -24dB to +24dB |
| Stereo Handling |
Maximum or Side Chain |
Studio Recording Effects: Expander / Gate
The stereo expander expands the dynamic range of the portion of an audio signal which falls below a given threshold. If you use the graph to control the settings, note that the graph shows only two visible nodes, allowing only the initial slope representing the expander to be moved. Its parameters are listed below.
| Setting: |
Range of Values: |
| Expander Threshold |
From -108dB to 0dB |
| Expander Ratio |
From 1:0 to 1:infinity |
| Attack Time |
From 0.1ms to 200ms |
| Release Time |
From 20ms to 1000ms |
| Master Gain |
From -24dB to +24dB |
| Level Detection Method |
Peak, Average, or RMS |
| Stereo Handling |
Maximum or Side Chain |
| Envelope Curve |
Soft Knee or Hard Knee |
Here are several common problems you can run into when using an expander:
| Problem: |
What to do: |
| The beginning of a sound is cut off |
Decrease the attack time |
| The end of a sound is cut off |
Increase the release time |
| Disturbing sudden change in background noise as the expander cuts in and out |
Lower the expansion ratio or increase the release time |
Stereo Handling:
The dynamics processors offer two choices for processing of stereo signals:
| Option: |
How it Works: |
| Maximum |
The left and right channels are adjusted equally according to the maximum of the left and right channel signal levels. |
| Side Chain |
The left channel volume alone is used to drive the effect, which is applied only to the right channel. This can be used, for example, to automatically lower the level of background music |
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