You can't set up the compressor without listening to everything else going on, but if you would like some ball‑park figures, ratio could be anything between 2:1 and 5:1, depending on how compressed you want it to sound and what 'knee' characteristic the compressor has. In fact, with lower ratios, you often can’t hear the compressor working at all. Attack & Release. If you go higher, the vocal will most likely end up sounding smashed. If you have a semi-constant level of the vocal at -1dB it will become compressed so that it only reaches … Say we had a downward compressor with a ratio of 3:1 and a threshold set at 0 dB. For every signal that goes over the threshold, it gets compressed according to a certain ratio. I usually set the compressor on my preamp to a ratio of 2:1, with a threshold of – 20, a release of 0.3 and a makeup gain of 2. Threshold depends on your levels, but I usually keep the ratio pretty high (6:1, 8:1) depending on if all the vocals are sent to a stereo bus "later" on. In a standard compressor (which is downward), a ratio of x:1 attenuates signal to a level of 1 dB above the threshold for every x dB it crosses. For example: A compressor with a threshold at -10dB and a 3:1 ratio is a nice starting point for vocals. Take a listen to the difference between high and low ratio compression on a drum kit: Low ratio (1.5:1) High ratio (10:1) Notice how much more aggressive the high ratio compression sounds. Often misunderstood, compression ratio simply specifies the amount of attenuation to be applied to the signal. Compression Ratio. To understand this, let’s look at an example. Rap vocals come out best if you use a fast attack and release on your compressor. You will find a wide range of ratios available depending on the type and manufacturer of the compressor you are using. The attack setting on a compressor decides how much time it takes for the compressor to compress at full force. How much compression occurs is controlled by the ratio. If you don’t have a pre amp that allows you to set the compressor, you can always get an external compressor (highly recommended) or not use one at all. Just like the original, you can push in all buttons for “Nuke” mode for explosive results — perfect for hard rock vocals. The compression settings then depend on the effect you're trying to achieve and what else is going on in the mix. Now, I have found that a good ratio for vocals is 3:1. If you go lower than that, you may not get the compression needed. The low ratio compression is much more natural and transparent. Four ratios are selectable via push-buttons (4:1 and 8:1 for compression, 12:1 and 20:1 for limiting).