Buzz Audio SOC-1.1 Stereo Optical Compressor


 Audio compressors that use a light source to control a Light Dependent Resistor (LDR) are not new, and indeed there are many classic optical compressor designs. The design goal of the SOC-1.1 was to further enhance the attributes of optical compression to provide the user with alot more functionality as well as improve the compressor response to real world audio signals. We have carefully examined the characteristics of the LDR and developed a truly unique process to control it. This process we call the Differential Drive Side Chaintopology (DDSC).

The DDSC circuit separates the positive and negative audio waveform in the compressor side chain and processes them in identical but electrically opposite paths. The resulting control signals are applied to two separate LED (light emitting diode) and LDR elements of our own design, one for positive, the other for negative signals. What this achieves is a compression characteristic that is more "in tune" with the audio source because the attack and release time settings are applied independently to the positive and negative elements of the signal, not just to the combination.

As far as we are aware, no other audio compressor in the market today employs this technique. The benefits of the DDSC design are most apparent when compressing low frequencies such as bass guitar and kick drums, but the SOC is equally at home on just about any audio source you can throw at it.

A common problem with older opto compressor designs (and many modern ones too) is the inherent slow attack time of the LDR elements. A unique speed up circuit within the DDSC effectively reduces the attack time to less than 1mS when the SOC is in FAST attack mode. 

We believe this is the fastest attack time of any LDR based compressor on the market today.

All the features available on the SOC allows users to create many different flavours of compression, from full on squash to just gentle leveling. A very useful piece of kit destined to become a classic. Checkout what some of our users say...

  • Controls for Attack, Release, Ratio, Drive and Output Levels.
  • Unique Differential Drive Side Chain design.
  • Probably the fastest optical compressor ever made.
  • Big knobs, large LED backlit VU meters (no bulbs to change).
  • Separate power supply regulators for audio/sidechain sections.
  • Each channel individually power regulated.
  • Auto bypass/mute relay when power lost.
  • Electronically balanced inputs and outputs on XLR.
  • Gain reduction metering that doesn't drift.


  • Music recording and mixing
  • Post production studios
  • Voice overs and dialog
  • Classical music styles
  • Live sound

Max Input/Output Level = +23.5dBu. 
      Measured with 2k ohm load and 0dB output gain makeup. 
Frequency Response = 4Hz to 250kHz. 
      -3dB points with no gain reduction. 
Slew Rate = 20V/uS
Harmonic Distortion = less than 0.008%. 
      Measured 100Hz to 10kHz with no gain reduction. 
Harmonic Distortion = less than 0.03%. 
      Measured 100Hz to 10kHz with 20dB gain reduction, Attack-AUTO, Release-16 
Residual Output Noise = typically -90dBu, -100dBu A wtg. 
      No gain reduction, 0dB output gain makeup, 150R input source impedance. 
Channel to Channel Crosstalk = below noise. 
      150R source Z on  measured CH-A, +20dBu applied to CH-B, 100Hz to 10kHz. 
Standard Operating Level = +4dBu = 0 VU meter display. 
Size = 2 Unit 19" rack mount, (482Wx88Hx250D).
Power requirements = 230V/115V selectable, IEC detachable power cable.

Specifications are typical of a production unit and are subject to change without notice. 
0dBu reference = 0.775 volts RMS.