The main difference between transient shapers and compressors is that transient shapers are threshold-independent, while compressors are threshold-dependent. This means that transient shapers are meant for input signals that are dynamic, such as the snare recording of a Jazz drummer.
With sample-based music, in which all of your drum hits are of the same amplitude, it would at first seem like a compressor is capable of applying the same type of processing as a transient shaper. However, there are a few key differences in the types of processing these devices can apply, and the way in which their controls function. At the end of this short guide I'll also explain when it's appropriate to use each type of device.
Types of Processing
A transient shaper is capable of applying mixed forms of dynamics processing to a single transient. For example, it can apply compression and expansion to the same transient at different points in time. You can apply expansion to the initial transient to give it more bite, and also apply compression to the transient's tail to tighten it up.
Many compressors are capable of switching into an expansion mode, but they are then acting as expanders, and not compressors. Additionally, compressors that are capable of swapping between these two processing modes cannot apply mixed compression and expansion to the attack and release of a transient; the entire input signal either gets compressed or expanded when it crosses the compressor's threshold. Compressors trigger when their input signal passes a threshold, while transient shapers trigger based on the rate at which their input signal level increases.
Controls
The other difference between transient shapers and compressors is the way in which the attack and release controls work. The attack on a transient shaper allows you to control the amount of downwards compression or upwards expansion applied to the initial transient. On a compressor, the attack controls the time it takes to apply the downwards compression.
The release on a transient shaper allows you to control the amount of downwards compression, or upwards expansion applied to the decaying transient, which can really help to thicken the tail of the signal or tighten up the sample. A compressors release determines the amount of time it takes for the compressor to stop compressing the input signal once it’s fallen back below the compressor’s threshold.
Use the Right Tool for the Job
The real question is, when are you meant to use a transient shaper, and when are you meant to use a compressor? As a rule of thumb, use a transient shaper when you're trying to shape the character of a dynamic signal's transients during their attack and release phases. Compressors allow you to apply time-based gain reduction to your input signal as it crosses a threshold, and they often come with a variety of controls that allow you to fine-tune this process. For an in-depth guide on how to use compressors, check out “The Ultimate Guide to Compression.” It will allow you to start tastefully applying compression to your tracks, and take advantage of the many dynamics shaping possibilities that compressors provide.
