The Amtec BC-5A Band Compressor is an easy to use 500-style analogue
dynamic equalizer capable of changing its frequency response according to the
incoming audio signal. It lets to control unevenness in the selected  part of the
spectrum by boosting the selected band during low-level signals and
dynamically reducing it when the signal in the band is excessive.

Depending on the band choice, the Band Compressor can help to make
instruments or voices sound bigger and fuller, with more body and thickness,
but without undue boominess or make them brighter and more present  with a
sparkle, brilliance and clarity, but without harshness, sibiliance and listening
The bands of operation range from low frequencies with shelving characteristics to peaking low midrange (centered at 240Hz)
or high midrange (centered at 3.4kHz) to high frequency shelving. One band is destined to work at  low and high frequencies at
the same time offering automatic "loudness" control, dynamically applying bass and treble boost at low volume levels.

The BC-5A operates only in one of the six selectable bands (the low frequency shelving filter offers internally selectable three
frequency point options, so in total there are 8 band settings to choose from) and allows to boost or  attenuate the signal in the
band and, additionally, to automatically reduce the gain in that band. The static frequency response is set by the EQ TRIM
control, which works as a typical EQ gain knob. Its range is from 20dB of  cut to 12dB of boost. This knob sets the basic
frequency response of the unit. The level of the band can be then automatically reduced by the use of the BAND
COMPRESSION knob when the energy in the band is xcessive.  The dynamic range is reduced only in the selected band, the
rest of the signal is not altered.

The BC-5A uses parallel processing, where filtered, compressed (using FET gain reduction element) and phase manipulated
input signal is combined with the direct unaltered path, resulting in minimal signal degradation. It  adds filtered signal to the
direct signal for boost or substract it for cut.

Apart from the hardwired bypass (using a relay) there is a facility to mute the direct sound, so that only the processed part can
be heard to observe what is actually being added (or substracted) to the signal.
It can be used as a problem solver that processes only the troublesome band
and controls difficult frequencies, leaving the rest of the incoming signal
untouched, maximizing signal integrity with no artifacts, transient  distortion,
pumping or over-processed sound.
It can also be used creatively by applying a strong emphasis on a certain
frequency range and controlling any overboost at the same time. It allows for
making voices and instruments to stand-out sonically and to cut through  the

It can be used to control boominess on certain instruments, to control
proximity effect or pops on vocal tracks or,  when set for operation in the
higher bands, to control high frequency spikes like esses or any excessive
treble  information.

Sources that require spectral enhancing can greatly benefit from boosting a
band of interest quite heavily and then letting the band compression to take
care of any excessive boost.
Instead of boosting an important band with an EQ and then taming it with
another device, the user can do it all using only the BC-5A with minimal signal
Amtec BC-5A User Manual