Chameleon Labs 7721 Stereo VCA Compressor

No longer available at zZounds
Glue your tracks together with this stereo bus compressor! Chameleon Labs' 7721 gives you control over soft/hard knee, peak/RMS detection, blend, and more.

Proudly made in Seattle, Washington, USA, the Chameleon Labs 7721 Stereo VCA compressor is a powerful analog processor designed to make your tracks sound more compact and powerful. When designing the 7721, Chameleon's engineers started with a clean sheet of paper and deeply evaluated the details associated with developing a bus compressor for the modern studio. Basing detection and voltage control on a voltage control amplifier (VCA) topology and designing a circuit that provides low noise and transparency, the team created an acoustic "glue" that is capable of consistently delivering punch and loudness to the signal.

Hear the 7721 bus compressor on drums and full mixes in zZounds' demo video:

Marcelo at Chameleon Labs takes you on a deep dive into the 7721 compressor's design:

The 7721 provides a classic set of adjustable settings as well as controls only available on esoteric compressors, including:

Soft Knee / Hard Knee:

Allows you to change between a softer-arriving compression effect and a faster-arriving, limiting type effect.

Peak / RMS:

This control allows you to choose between the Peak and RMS detection schemes that are quite different. Peak detection engages the compressor by monitoring peak or instantaneous voltage signals. RMS engages by looking at the average energy in the signal and comparing it to the threshold setting. Very different modes of operation that provide great solutions for specific problems.

High Pass Filter:

When the HPF is read more engaged, the compressor doesn't affect frequencies below the cutoff. When the Side Chain input is engaged, the filter is applied to Side Chain detection signal. If you decide to use a Side Chain signal as the compression trigger signal, you can use the High Pass Filter to high-pass the audio signal and avoid pumping effects.

Classic Controls:

Threshold / Attack / Release / Ratio - Low ratios provide a nice starting place for master transparency, 4:1 provides more color and higher ratios for a tougher sound full of character. Try using the Attack and Release controls to respond to tempo and feel of a track.


This control allows you to blend, or mix, the original uncompressed signal with the compressed signal providing another tool you can use to obtain your desired objective.

VU Meter:

Monitor Input, Outputs and Gain Reduction levels.


- Stereo compressor with VCA-based signal detection
- Super low noise, IC based input section
- Side chain input allows a separate source to be used as the compression trigger
- IC based, ultra-low noise output stage
- VU meter for Input / Output Level and Gain Reduction monitoring
- Super low noise internal power supply
- Selectable high pass filter
- Threshold, Attack, Release and Ratio controls
- Selectable detection type Peak or RMS
- Selectable compression types: Soft or Hard Knee
- Blend control allows you to mix the compressed audio signal with the original signal
- Proudly made in the USA in Seattle, Washington
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On Switch: Turn Unit On - VU Meter Light is ON

Compression: Insert compression circuit or bypass

Side Chain: Use Side Chain Input for triggering

Compression: Soft or Hard knee compression type

Detection: Peak or RMS

High Pass Filter: 60, 90, 130 or 200 Hz high pass filter. When the HPF is engaged, the compressor doesn't affect frequencies below the cutoff. When the Side Chain input is engaged, the filter is applied to Side Chain detection signal.

Threshold: Applied between -15dB and +15dB

Attack: Attack time in milli seconds - .1 / .3 / 1 / 3 / 10 / 30

Release: Release time in seconds - .1 / .3 / .6 / 1.2 / 1.5

Ratio: Compression ratio selection 1.5 / 2 / 4 / 8 / 10

Blend: Full Dry equivalent to 0% compression, Full Wet equivalent to 100% compression

Output Gain: -60dB to +20dB Output Level control

VU Meter controls (L&R): In - Input / Out - Output / GR - Gain Reduction

Input (Female XLR): 50 kOhm

Side Chain Input (Female XLR): 50 kOhm

Output (Male XLR): 200 Ohm

Noise Specification: <-100dBu Input Terminated with 600 Ohm, compressor ON and Output Gain set to 0dB

Frequency Response: 20Hz - 20kHz +/- 0.25dB

Headroom: > 20dB output level

Dynamic Range: 100 dB per AES17 Standard

Common Mode Rejection: 100Hz - 10kHz >90dB

Input and Output Impedance: >10kOhm / <50 Ohm

Red Input Gain: Input Overload

Red Output Gain: Output Overload

Power Supply: 100V - 240V (50/60Hz): Switch mode power supply, fully shielded 3-amp peak output capability, quiescent consumption 0.5 Watts

Mechanical: 1RU Steel enclosure, Aluminum front panel, Laser etched graphics, Milled aluminun knobs

For support or warranty questions, please contact the manufacturer:

No longer available at zZounds

In most cases, a product is unavailable because it has been discontinued by the manufacturer