Manual for Noise Gate

Noise gate plugin based on spectral subtraction

You can download the spectrum subtracting noise gate VST plugin at it's page. Put it before effects which highly amplify input noise like compressor or guitar distortion.

How it works

Using noise filtering schemes, which apply spectral subtraction, like this plugin, assume that you have or can obtain in some way a short noise sample, the sample without instrument or voise signal, only noise. To obtain it you need first of all to activate your whole sound processing chain, which gives hearable noise at output. You need it to listen when only the noise presents and when the mean signal starts. Of couse you can just know it without listening. But it's better to monitor.

If you are filtering guitar (most complex case), then you will take strings in your left hand to keep sounding only the noise witch stays when you are touching strings, but are not playing. Just take such a piece (1-2 seconds) of signal gently before playing, and it will be possible to use 7AMP.NET Noise Gate then.

When that noise sample starts (at the beginning of a track in most cases) push down the "Peek" button to make 7AMP.NET Noise Gate study noise amplitude-frequency characteristic. You will watch the process of studying noise on the spectrum indicator. Pink (noise) levels will raise to blue (signal) levels in 1-2 seconds. And you will hear the noise going out, but not at all. Then push the "Peek" button up to stop studying process.

Warning! Push up and down the "Peek" button smartly to avoid studying of instrument or vocal sound as noise, because it will reduce filtering quality.

To completely remove noise, tune the "Level" knob. Too high level values will result in bad amplitude-frequency dynamics of output sound. Too low will not allow to remove noise completely.

Some technical details

Recursive Fourier Transform is usually used in a spectrum subtracting schemes. Though it works slow in comparison with Fast Fourier Transform, it allows to avoid splitting signal to blocks and caused edge effects of that blocks. Also RFT makes possible using longer blocks which gives higher frequency resolution. But these features of RFT are performance payed, so this plugin uses scheme of 7 Fast Fourier Transform elements instead to avoid that edge effects and make block transitions smoother without using RFT. But this is still slow enough.

Warning! Using Fourier Transform makes the plugin sensitive to the sampling frequency. No problems. It continues to work fine, but characteristics may and will change. By changing sample frequency you makes saved noise information inappropriate and will need to re-peek noise. By making sampling frequency higher you will reduce frequency resolution of the plugin, especially at low frequencies. It will cause worse filtering. Big resolution range will be used at higher frequencies witch in fact do not present in signal at all. I tested the plugin at 48000 kHz and recommend it for use. 96000 kHz sampling frequency is acceptable too.

Warning! Using FFT makes the plugin sensitive to the input signal block size. Though some internal features prevent edge effect from appearing with any block sizes, the size of 512 samples is ideal and preferable.

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