When you paint a window frame it is clear to the eye when the brush strays… since you see the paint on the window. Our hearing is usually not as good as our vision, and further singing or playing guitar is a little more complicated then staying in between the lines when painting. So it is easy to stray in the sound spectrum and when it happens we might not even notice.
Compression is a tool to remove the errant paint off that window. Though instead of literally removing the error a compressor, compresses any errant paint that went on the window, compressing it small enough so that it never exceeds the dimensions of the window frame, paint that always stayed between the lines is not effected at all (the result is the loudest sounds are made quieter and everything else is not affected).
Besides setting threshold (the db level of where you want the compression to happen) and ratio (the amount of compression you want to occur above that line), the other important elements are attack and release times. These are the amount of times it takes the compression to kick in and kick out. If they are too long or too short you have problems. In general, if the attack time is too fast you lose drums. If you want to preserve the original source sound you want to set the slowest attack and release times possible.
It should be noted that this compressed/concentrated audio cannot be resurrected by adding water so don’t overdo it with compression. And while mostly all cds are mastered, and music is often recorded and mixed with compression I think you should experiment for yourself whether you it is what you want. It is possible to exist without it if you record with precision.
Also a close relative to the compressor is the limiter. Limiters are like extreme compressors. Whereas a compressor draws a somewhat malleable line of where your audio should not cross by setting both a threshold and a ratio, a limiter is a much more certain ‘audio shall not pass this level’ line where only the threshold is set.
There are hardware compressors and software compressors. Logic Pro X, Protool but also cheap or free DAW as Cool edit pro and N-track come with bundled compressors that have real time preview so you can decide if it is right for you. T-racks is a complete software mastering studio program with built in compressor, limiter, and equalizer which has some really good presets that provide good starting points (I recommend downloading the demo to get an idea of what mastering/compression can do to your sound).
Any of these options would probably be the easiest avenue for the pc-musician. Cool Edit and Ntrack also come in demo form, the later being a fully functional demo…. so experiment for yourself and make your own decision about compression. And remember that not all good art stays between the lines…
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