Waves Abbey Road EMI TG12345 User Manual - page 6
Waves / Abbey Road TG12345
User Guide
6
Feedback Compression
The signal entering the compressor is sent to the VCA. The output of the VCA is then split: one copy
goes to the output, while the other is fed back to the VCA via a sidechain circuit. See the image
below:
Sidechain High Pass (SC-HP)
As explained in the Feedback Compression section above, the input signal is fed to back to the
VCA. Generally, the more energy you have in the sidechain, the more compression you get; but if
you apply a high-pass filter to remove low energy from the signal, the result is less energy when
low-frequency energy is present, hence less compression. In the case of a bass guitar, for example,
the abundance of low energy entails lots of compression; but if a high-pass filter is applied on the
sidechain, the VCA will identify less energy on the low bass notes than there is in the actual input
signal and will therefore attenuate the signal less, allowing more low frequency.
Sidechain Voltage
The sidechain section of the TG12345 converts the signal from AC to DC, with the VCA controlled
via the DC current. The higher the DC current, the more compression you get. The sidechain
voltage can range from a couple of mV to 15 V. The amount of compression for each volt is
represented in the VCA graph above.