TL Audio VP-1 - Manual (Page 15)

This switch allows a choice of two compressor response types - Hard or Soft Knee.
Soft knee mode means that once the signal has exceeded the threshold, gain reduction
is introduced gradually, since the response curve of the compressor around the
threshold is gentle. This results in a more subtle and musical type of compression
effect. In “Hard Knee” mode, the curve is more severe, so that signals above the
threshold are “squashed” more aggressively. This yields a more audible and
pronounced compression effect.
4.23 Compressor Opto Mode.
The VP-1 offers two distinct and independent types of gain control circuit. The
normal mode employs the trademark TL Audio transconductance amplifier circuit, as
featured in many other TL Audio products, notably the C-1 compressor. This circuit
uses a solid state transconductance amplifier to accurately control gain, with a triode
valve stage in the gain make-up circuit to add warmth.
The VP-1 ‘Opto’ mode replaces the transconductance amplifier with an optical gain
control circuit, with the valve still active in the gain make-up circuit. The opto circuit
uses a LED/light dependent resistor device to control gain, which yields a slightly
more coloured sound with a slower response time. Many vintage compressors employ
opto designs, and its inclusion on the VP-1 allows a much wider palette of
compression sounds to be obtained.
4.24 Compressor
Hold.
The Hold facility on the VP-1 delays the onset of release for approximately 10msec
after the input signal reduces below the threshold. This feature helps to reduce the
distortion commonly caused when using a compressor with a short release time to
process a low frequency signal, for example a bass guitar, where the compressor
attempts to modify the gain during each half cycle of the input waveform. If distortion
is experienced under these circumstances, activate the hold facility.
4.25 Equaliser
Section.
The VP-1 boasts a four band valve EQ stage with low and high frequency shelving
and two fully parametric mid bands, giving an ideal combination of simplicity and
flexibility. Before switching the EQ into circuit, it is advisable to set the cut/boost
controls to their centre, or flat, position. The EQ is brought into circuit with the
overall “EQ-ON” push switch, signalled by a green LED. Like the compressor
section of the VP-1, the EQ stage can be pushed to quite extreme settings without
upsetting the tonal character of the signal. Many EQs can sound unpleasant and
unnatural when used in extreme ways, whereas the VP-1 positively relishes being
pushed hard.
4.26 LF and HF shelving bands.
Both the LF and HF bands offer four switched shelving frequencies:
LF shelving at 60Hz, 120Hz, 250Hz and 500Hz