New! Introducing the Waveulator zero attack zero release limiter/saturator.

"Waveulator" is a combination of the words "wave" and "modulator" and is used to describe a zero-attack zero-release limiter or saturator to provide final protection limiting and loudness enhancement. The Waveulator provides overshoot-free "wave bending" ranging from soft saturation, to hard brickwall, to extreme "reverse" limiting. The Waveulator is not a "color" device, it's role is to provide level control and crest factor reduction to allow increases in RMS level and perceived loudness or, in moderation, protection limiting before final conversion.

The Waveulator uses familiar Threshold, Ratio/Hardness and Make-up Gain controls. The Waveulator, unlike conventional dynamics processors, does not operate on signal history and instead processes the real-time waveform. There are no attack-release controls because there is zero attack and release time. Instead of using diode or Zener based clamps, the Waveulator uses THAT2180 VCAs operating as modulators. The Sidechain, which is a "thresholded-peak-skimming" full-wave rectifier, is used to modulate the VCA's control ports. The rotation point of the "compression" curve on the real-time waveform is set by the Threshold Control. The amount of gain reduction above the rotation point is controlled by the Ratio/Hardness control. A Make-Up Gain control provides a fixed gain offset to set the final peak level.

Diode-based clippers compress above threshold and follow a logarithmic curve above their rotation point. Zeners have a harder knee. The result is a large reduction in level initially followed by a smaller reduction thereafter. The initial "bite" into the waveform is large and, above threshold, distortion rises rapidly. Initial experiments with the Waveulator used linear modulation with a log-based detector feeding the VCA's exponential control ports. The combination of the two "laws" produce a linear transfer function. It was later found, quite by accident, that a linear detector feeding an exponential control port produced far less audible distortion. With an exponential response the initial "bite" into the signal is small and then increases rapidly as the threshold is exceeded by a larger amount. The Waveulator's exponential response is similar to dBx's "Over Easy"® except that it processes the real-time waveform. The result provides far more gain reduction prior to introducing distortion.

The Waveulator has the following features:

• Balanced THAT 1246 inputs.
• Balanced THAT1646 outputs.
• Adjustable Limit Threshold. Can be calibrated in -dBFS based on the converter's 0 dBFS point.
• Ratio/Hardness control. Controls the slope of waveform "compression." Can range from soft gentle rounding to reverse limiting. "Reverse limiting" is when increases in signal cause slight decreases in output level.
• Make-Up Gain. Provides gain adjustment to set final peak level.
• Threshold LED. Illuminates whenever the threshold is exceeded by 0.5 dB.
• Bypass relay. Provides a "soft" bypass looping the input line receiver to the output driver for Processed/Bypass comparison. LED output provided with 2K21Ω current limiting.
• Meter Outputs. Three outputs. Voltage Output scaled at +2.4V for 10dB gain reduction. Two Current Outputs 1 mA FS at 5 dB and 1 mA FS at 10 dB gain reduction. (Requires that the customer install two resistors based on the internal resistance of a user-supplied 1 mA meter. Maximum meter internal resistance should be less than 1.2KΩ.
• Internal +24V relay supply. On-board 78L24 regulator isolated from audio ground.

Mechanical and Power Specifications

• Board Size: 6.3" x 3.3" Mounting holes: M3 on a 6" x 3" pattern. Assembled height: Approximately 1" not including stand-offs.
• Power Requirements: ±15 to ±18V (max) approximately 130 mA (no signal current).

Audio Specifications

• Inputs: THAT1246. Input Impedance 24KΩ differential, 18KΩ common mode. Maximum input level +27 dBu.
• Outputs: THAT1646. Differential output impedance 50Ω nominal. Maximum output level +27 dBu.
• Noise: -99 dBu, dynamic range 126 dB in bypass; -91 dBu, dynamic range 118 dB process in. (Makeup Gain, Threshold and Ratio at "0." Input terminated in 100Ω.)
• Residual Distortion: THD In bypass 0.0006% typical; Process In, no effect, 0.015% typ. at 1 kHz 0 dBu input and output.
• Introduced Distortion: +8 dBu Input at 1 kHz. Threshold at minimum. Ratio/Hardness at maximum: H3-H9 odd-order approximately 22% total, H2-H8 even-order 0.06% typical; Ratio at 50%: H3-H9 odd-order approximately 10% total; Ratio at 25%: HD3-HD9 odd-order approximately 5% total.
• Frequency Response: DC-coupled in bypass. Process In: -0.2 dB +0.0 dB 10 Hz - 40 kHz. (Measured with balanced outputs. Single-ended output terminations have a -3 dB point at approximately 1 Hz.)
• Threshold Adjustment Range: Approximately -2 dBu to +27 dBu. Maximum clockwise rotation can be calibrated to converter 0 dBFS.
• Threshold Scale factor: Vthreshold = Vin(RMS)/1.736. +27 dBu = +10VDC.
• Make-up Gain Range: 0 to +12 dB.

Note: Noise measurements are for a 20-20 kHz bandwidth and are unweighted. Maximum level specifications are for balanced inputs and outputs with ±15V supplies.

To learn more about the "Waveulator" visit the Pro Audio Design Forum construction thread.

The KA-Electronics Waveulator is sold as either a bare PC board, a "kit" (including  2 THAT1246, 2 THAT1646, 2 THAT300 and 2 THAT2180B), and the assembled and fully-tested module shown here.

A Mouser Electronics Project Manager bill-of-materials is available for DIY builds.