MSP; "A Primer on Compression" - Peabody Computer Music

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Tutorial 3Tweaking Compressionadjustments to the release timer based on the input signal. Signals below thefreeze level will not trigger any amplification. Signals above this but belowgating level will have a slow release. Progressive release speeds up the releasetime on stronger inputs. This means that softer signals (where the ear is lesssensitive to dynamic change) will not be as compressed as loud ones.LimEnabledputs an absolute limit on the strength of the output signal. This prevents asignal overload when the controls are set for punching.Parameter MessagesThe omx objects from Octiv, Inc. send messages from the third outlet when parameters arechanged. These are in parameter lists, which contain 7 fields:1. Scope 0 = global, 1 = presetable, 2 = end of list.2, Name of parameter.3. Current value.4. Maximum value.5. Minimum value6. Display value.7. Units – this is “arbitrary” for most items.The parameter values are arbitrarily scaled, most from 0 to 100. Some of these can beconverted to familiar units. Any dB parameter can be converted by looking at the valueshown when set at 0 – that’s the minimum value (100 corresponds to 0 dB). Divide 100 bythis value to get the scaling factor. Then to set a value, add the absolute of the minimum andmultiply by the absolute of the scaling factor, like this:• To convert agcThreshold (range from –36 to 0) use an expr object with the following arguments:(36 + $i1) * 2.77.• To convert ngThreshold (range from –90 to 0) use an expr object with the following arguments:(90 + $i1) * 1.11.It’s probably easier to capture the numbers coming out in the parameter messages anddisplay those.12
Tutorial 3Tweaking Compression• Ratio uses exponential values. To convert the numbers given to ratio use an expr objectwith the following arguments: ln($f1) / ln (1.04).PresetsWith so many parameters, some method for recalling combinations of settings is essential.The compressors have a few presets built in (selectable using the ChoosePreset message), but theultimate solution will be to save the entire setup in a coll or pattr object. The SaveSettings messagewill give you a dump of all of the parameters.MeteringThe right outlet provides gain metering if enabled with the meters message. The outputs are alist ready to be connected to a multislider object. The list for the omx.comp~ shows left and rightvalues for AGC gain, noise gate and limiter. The meterRate message determines how oftenthese are sent. Alternately, you can get the values using the meterData message. The meters forthe 4-band and 5- band compressors are quite elaborate.13
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MSP; "A Primer on Compression" - Peabody Computer Music

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