Phoenix SC Stereo Tube Compressor

Thermionic Culture has added a third Phoenix stereo tube compressor to the range; the Phoenix SC, or Side Chain, a stereo compressor that can be used as a pair of mono compressors. The Phoenix SC is virtually identical to the standard Phoenix, but in addition has the side-chain filter section from the Phoenix Mastering Compressor (MC). The side chain filter provides 75Hz & 150Hz, but more permutations are possible when the MC is used in stereo mode with the link switch engaged. The SC model has the same higher gain structure as the standard model, which means it can slam more than the Mastering model, which makes it more useful for individual tracking or mixing functions, but added the extra versatility of having one of the best two-bus compressors available for your stereo bus due to the chain filters.

The Phoenix has a soft knee or "variable mu" characteristic, in that the compression ratio increases with the amount of compression being used. Initial compression is 1.2:1 increasing to 5:1 at 15dB compression. The Phoenix is being updated continually and this unit is the 2009 version (suffix QSC) with sidechain filter. The sidechain works by filtering out bass frequencies from the compressors detector circuit and this makes the compression less sensitive to the low frequencies present in the audio signal. It is due to the nature of bass frequencies that this is a desirable effect. Bass frequencies tend to contain a lot of the energy present in a full band signal and large fluctuations in the amplitude of these frequencies can tend to dominate the performance of the compressor.

A classic example is found when using a compressor over the mix bus. If the music contains a bass instrument that is not in all the way through the mix, it is noticeable that the overall volume of the other instruments in the mix can go down when the bass instrument is introduced. This is especially noticeable when using heavy compression. The sidechain can also be useful on single instrument sources, perhaps a vocal that needs to be dynamically controlled in the mid-range frequencies for example.