Gain

Name

Gain -- apply gain or attenuation; normalise/equalise/balance/headroom

Synopsis

gain [-e|-B|-b|-r] [-n] [-l|-h] [gain-dB]

Function

Apply amplification or attenuation to the audio signal, or, in some cases, to some of its channels.

Without other options, gain-dB is used to adjust the signal power level by the given number of dB: positive amplifies (beware of clipping), negative attenuates. With other options, the gain-dB amplification or attenuation is (logically) applied after the processing due to those options.

Given the -e option, the levels of the audio channels of a multi-channel sample are "equalised", i.e. gain is applied to all channels other than that with the highest peak level, such that all channels attain the same peak level (but, without also giving -n, the audio is not "normalised").

The -B (balance) option is similar to -e, but with -B, the RMS level is used instead of the peak level. -B might be used to correct stereo imbalance caused by an imperfect record turntable cartridge. Note that unlike -e, -B might cause some clipping.

-b is similar to -B but has clipping protection, i.e. if necessary to prevent clipping whilst balancing, attenuation is applied to all channels. Note, however, that in conjunction with -n, -B and -b are synonymous.

The -r option is used in conjunction with a prior invocation of gain with the -h option - see below for details.

The -n option normalises the audio to 0dB FSD; it is often used in conjunction with a negative gain-dB to the effect that the audio is normalised to a given level below 0dB. For example:

gain -n

normalises to 0dB, and

gain -n -3

normalises to -3dB.

The -l option invokes a simple limiter, e.g.

gain -l 6

will apply 6dB of gain but never clip. Note that limiting more than a few dBs more than occasionally (in a piece of audio) is not recommended as it can cause audible distortion. See the compand effect for a more capable limiter.

The -h option is used to apply gain to provide head-room for subsequent processing. For example, with

gain -h bass +6

6dB of attenuation will be applied prior to the bass boosting effect thus ensuring that it will not clip. Of course, with bass, it is obvious how much headroom will be needed, but with other effects (e.g. rate, dither) it is not always as clear. Another advantage of using gain -h rather than an explicit attenuation, is that if the headroom is not used by subsequent effects, it can be reclaimed with gain -r, for example:

gain -h bass +6 rate 44100 gain -r

The above effects chain guarantees never to clip nor amplify; it attenuates if necessary to prevent clipping, but by only as much as is needed to do so.

Output formatting (dithering and bit-depth reduction) also requires headroom (which cannot be "reclaimed"), e.g.

gain -h bass +6 rate 44100 gain -rh dither

Here, the second gain invocation, reclaims as much of the headroom as it can from the preceding effects, but retains as much headroom as is needed for subsequent processing.