The only difference between the stereo compressor TM212 and the mono Compressor
TM112 is the side chain insert point that is not possible with the compact
stereo version. Since the stereo compressor uses the 2U module size, the side
chain insert connectors of the mono version are used for the right stereo
channel. This disadvantage is more than compensated by the compact size of the
device; five stereo compressors can be installed in a 1U high frame. Together
with an attractive price, this adds a new perspective for applying stereo compressors
to stereo audio chains. If the side chain insert is an important issue for you,
check the Stereo Mastering
Compressor TM222; another stereo compressor of the ToolMod series. The
TM222 is a 4U module that adds some special functions for stereo mastering and
a side chain insert as well.
Like the TM112, the TM212 is a feedforward controlled vca compressor with variable AC/DC converter. The Crest switch selects peak characteristics, RMS characteristics or a medium value, that offers excellent result for many applications.
The standard parameters Threshold, Attack, Release, Ratio and Gain have independent controls. The special functions Soft Knee, Envelope, and Autogain complete the feature set.
The threshold ranges from -32 dB to 15 dB, the ratio has a control range from 1:1, which actually disables the compressor, to 20:1, which is limiter operation. The attack time control can be adjusted from 0.1 ms to 30 ms; the range for the release time is 50 ms to 3 sec.
The Envelope function can reduce low frequency distortion with short, 'pump free' release time settings that is caused by regulation within the period of the audio signal. A special filter design, combined with dynamic modulation of the release time is controlled by the envelope pot that determines the upper limit frequency of this compensation.
The setting of the Soft Knee control affects the regulation in the level range around the threshold level. The scaling determines the transition range from 0 dB, equal to hard knee, to up to 12 dB. A setting of 12 dB causes a soft approximation to the regulation characteristics that are determined by the ratio setting over a range of 12 dB. Soft knee settings can result in higher compression rates and/or less negative side effects. In general, a higher loudness gain can be achieved using the soft knee characteristics.
The settings of the threshold and the ratio control together with the attack time determine the gain reduction and the output level of the compressor. The Autogain-Function avoids the need to correct the output gain accordingly and calculates the necessary gain from the settings of threshold, ratio and attack. Threshold setting above 0 dB cause no additional gain; however, the gain reduction is entirely compensated with any setting of the threshold control below 0 dB. Autogain is very precise with short attack time settings. With longer attack time settings, peaks can pass the stereo compressor without causing regulation. The necessary gain depends on the signal structure of the audio signal that cannot be calculated by the autogain circuitry without causing either delayed reaction or another unwanted regulation parameter. The attack time compensation is based on empirical values and operates with a tolerance of less than 3 dB with almost all real world audio signals. Autogain can be disabled; an additional manual gain control with +/- 20 dB control range exists as well.
The stereophonic AC/DC converter section calculates the level of the channels and uses the channel with the higher momentary value for regulating both channels dynamically. The reaction of both channels is precisely adjusted as well as the tracking accuracy of both audio channels.
The gain reduction display is a LED bar graph with 5 LED's and 20 dB range.
The TM212 Stereo Compressor is a 2U ToolMod module that fits into all ToolMod frames. As usual, horizontal and vertical versions are available.