Compressors 201 – Threshold

A compressor has a lot of knobs and settings. They can be confusing at first. In this blog I am going to talk about one of those knobs – Threshold.

A compressor is an automatic volume control. We try to make the signal somewhat the same, static. Without a compressor, we would have to do it manually, turning the signal down, then up, then down, etc. But with a compressor, it can do that job for us.

When a signal gets loud (and crosses the threshold), it turns it down. If there’s any makeup gain, it will turn the softer signals up making them louder (along with everything else, of course).

The threshold setting tells the compressor when to start working. Put a compressor on, say, a vocal track. Pay attention to the input signal on the compressor. Let’s say the input signal is -10 dB. Now set the threshold knob to -16 dB, and the Ratio 2:1. What we’re telling the compressor to do is this: Any signal that is stronger than -16 dB, I want it to compress (lower) the signal. When the signal crosses the threshold it will get cut (attenuated) in a 2 to 1 ratio. So in this scenario, the signal is coming in at -10, with the threshold set to -16 and a 2:1 ratio. This means 6 dB is going to get compressed in a 2:1 ratio. The signal will get cut down to 3 dB over. You can think 2 becomes 1, 4 becomes 2, 6 becomes 3, etc.

If the ratio was 10:1, the signal would get compressed more. The higher the number, the more the compression. If the signal crossed the threshold by 10 dB, then it would be reduced to 1 dB.

The threshold determines how much of the signal the compressor is going to affect. You can change where the threshold is set usually in two ways. Using the Dyn3 compressor/limiter, grab the orange arrow on the signal led and slide up or down. Or to the far right at the bottom, grab the threshold knob and set up or down.

TIP: If Pro Tools is your DAW, use the Dyn3 Compressor/Limiter (free). It helps to make understanding what and how a compressor works easier.

I hope this helps!

and HEY! Make it a great day!

Tim

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Compressors 103 – Going deeper

Today I’m going to go a little deeper into how compressors work. But first, I want you to do an experiment. This experiment will allow you to SEE what a compressor does. When I did this, things started to become a lot clearer for me. We have to listen differently when it comes to compressors. We are not listening for frequency, we are listening to dynamic changes (amplitude, loudness).

For this experiment it would be better to use a bass track. The reason for this is one, we ALWAYS use a compressor on a bass track and two, the reasons to use a compressor on a bass track is because we want to control the initial attack of a note and lengthen the sustain of the notes, as they fade out quickly. Try to use a track that has a regular-type bass line, not one that is super busy.

1. Find a bass track (or create one using a VI).  If a virtual instrument is used, use one that emulates a real bass guitar, not something like a synth bass. What is needed is a sound whose initial attack is strong (loud) and whose note decays after the initial onset of the note, like a real bass. Also, the track will need to be printed. For this test to work we need an audio clip, not a MIDI clip.
2. Put a compressor on the bass audio track.
3. Set the ratio to something higher, i.e. 6:1. Set a fast attack, i.e. 3 ms; fast release, i.e. 18 ms.
4. Lower the threshold until the meter shows roughly 8 dB of gain reduction. Then add some makeup gain. Set this to the amount being reduced. If the gain reduction meter shows 8 dB of reduction, set makeup gain to 8 dB. This way the volume remains the same.

What you should start to notice is that the initial attack of the notes (when the player first strikes the notes) no longer punches. Now the dynamics are a little flatter, smoothed out. The second thing you should notice is that the notes are more sustained. You will no longer hear the decay, but a nice solid note that holds out for it’s full duration of note value (i.e. quarter note, half note, etc.)

NOW, print the track again with the compressor engaged. What you should have are two printed bass tracks. One without compression and one with compression. Look at the differences between the two. The first track has a pronounced attack with high amplitude and fast decay. The second, the initial punch is now all or mostly reduced and the sustain of the note stays strong longer. Below is a picture of what this should look like. 

I have done exactly that here. I used an Instrument track with Trillian Bass module – played a bass line – printed it – ran compressor with 6:1, 3 ms attack, 18 ms release, 8 dB gain reduction, and 8 dB make up gain. I think this helps to drive home what a compressors job is. In this example my goal with the compressor was to lessen the attack and give it more sustain. If you want to see what the compressor does even more obvious than this, use the fastest attack possible, with 8:1 ratio, with a lower threshold for more gain reduction (10 dB).

I hope this helps – it did for me! Next time I will start to go into specific parts of a compressor, i.e. threshold, knee, attack, release, etc.

As always – HEY! Make it a great day!
Tim