PRESONUS Studio Channel [15/30] Operation

OPERATION

13 | PreSonus 2007

Why do you need noise gates?

Consider the compressed vocal example above and you now have a 20dB dynamic range for the vocal

channel. Problems arise when there is noise or instruments in the background of the vocal mic that became

more audible after the lower end of the dynamic range was raised (air conditioner, loud drummer, etc). You

might attempt to mute the vocal between phrases in an attempt to remove the unwanted signals; however this

would probably end disastrously. A better method is to use a noise gate. The noise gate threshold could be set

at the bottom of the dynamic range of the vocal, say -10dBu, such that the gate would ‘close’ out the

unwanted signals between the phrases.

If you have ever mixed live you know well the problem cymbals can add to your job by bleeding through your

tom mics. As soon as you add some highs to get some snap out of the tom the cymbals come crashing

through, placing the horn drivers into a small orbit. Gating those toms so that the cymbals no longer ring

through the tom mics will give you an enormous boost in cleaning up the overall mix.

3.2.2 Types of Dynamics Processing

Dynamics processing is the process of altering the dynamic range or levels of a signal thereby enhancing the

ability of a live sound system or recording device to handle the signal without distortion or noise, and aiding

in placing the signal in the overall mix.

Compression / Limiting

Punch, apparent loudness, presence…just three of many terms used to describe the effects of

compression/limiting.

Compression and limiting are forms of dynamic range (volume) control. Audio signals have very wide peak to

average signal level ratios (sometimes referred to as dynamic range which is the difference between the

loudest level and the softest level). The peak signal can cause overload in the audio recording or reproduction

chain resulting in signal distortion.

A compressor/limiter is a type of amplifier in which gain is dependent on the signal level passing through it.

You can set the maximum level a compressor/limiter allows to pass through, thereby causing automatic gain

reduction above some predetermined signal level or threshold. Compression refers, basically, to the ability to

reduce the output level of an audio signal by a fixed ratio relative to the input. It is useful for lowering the

dynamic range of an instrument or vocal, making it easier to record without distorting the recorder. It also

assists in the mixing process by reducing the amount of level changes needed for a particular instrument.

Take, for example, a vocalist who moves around in front of the microphone while performing, making the

output level vary up and down unnaturally. A compressor can be applied to the signal to help correct this

recording problem by reducing the ‘louder’ passages enough to be compatible with the overall performance.

How severely the compressor reduces the signal is determined by the compression ratio and compression

threshold. A ratio of 2:1 or less is considered mild compression, reducing the output by a factor of two for

signals greater than the compression threshold. Ratios above 10:1 are considered hard limiting.

Limiting

refers to the point at which the signal is restrained from going any louder at the output. The level of

input signal at which the output is reduced is determined by the compression threshold. As the compression

threshold is lowered, more and more of the input signal is compressed (assuming a nominal input signal

level). Care must be taken not to ‘over compress’ a signal. Too much compression destroys the acoustic