Beigel Sound Lab Envelope Controlled Filter


  • VCF Effect Foot Switch
    Electronically switches the filter section in or out of the audio signal path.If the switch is in OFF position, the effect can be foot-switch controlled.
    Works independent from the EXT switch.
  • External Effect Foot Switch
    Electronically switches an external audio signal processor into the audio path between the input preamp and the voltage-controlled filter. Distortion, phasing, flanging, compression, and other processors can thus be switched into the audio system without affecting the performance of the envelope filter or the filter sweep. If no EXT effect is connected to the EXT in jack, the EXT switch has no effect.
    If the switch is in OFF position, the effect can be foot-switch controlled.
    Works independent from the VCF switch.
  • Envelope Follower Onset (1-10)
    Adjusts the onset or "attack" time of the envelope follower. The onset can never be faster than the actual attack time of the musical input signal.
  • Envelope Follower Decay (1-10)
    Adjusts the decay time of the envelope follower. The decay time can never be shorter than the actual decay time of the musical signal.
  • Envelope Follower Sensitivity (1-10)
    Adjusts the envelope follower response to the input signal level.
  • Envelope Follower Sweep (Lin/Log)
    Changes the way the envelope follower responds to your playing dynamics.
    Lin position: gives the widest range of dynamic response, so that playing soft will create much less envelope drive than playing loud.
    Log position: has the effect of "compressing" the envelope response, so that you get a consistent envelope response, much less sensitive to your playing dynamics.
  • VCF Sweep Start, Stop (1-10)
    The Start and Stop controls determine the direction and extent of the filter sweep.
    Start: with no envelope (zero signal) the filter corner frequency is determined by the position of the Start control.
    Stop: with full envelope (overload light goes on) the filter corner frequency is determined by the Stop control.
    In other words, the filter sweeps from START to STOP as the envelope goes from zero to its maximum value. If the STOP control is set higher than the START control, the filter sweeps upward, if the STOP control is set lower than the START control, the filter sweeps downward. If the START and STOP controls are both set to the same value, the filter frequency does not change at all: the unit then performs similar to a one-channel parametric equalizer.
  • VCF Range (Lo/Hi)
    Allows the filter to sweep over two overlapping ranges.
    LO position sweeps from 150Hz to 5KHz (Start and Stop controls set at 1 and 10).
    HI position sweeps from 350Hz to 12KHz.
  • VCF Mode (LP/BP/HP)
    Selects the filter characteristic desired for the musical effect.
    LP (Low Pass): passes signals below the filter's cutoff frequency.
    BP (Band Pass): passes signals in the region of the filter's cutoff frequency.
    HP (High Pass): passes signals above the filter's cutoff frequency.
  • VCF Peak (1-10)
    Varies the amount of emphasis at the filter's cutoff frequency. The higher the control setting, the greater the "peak" in the filter's audio response. This will produce a more pronounced filter effect.
  • VCF Peak (Man/Env)
    Allows control of the filter "peak" by eather the peak control or the signal envelope.
    MAN position allows manual control by the Peak Control knob.
    ENV position controls the filter peak by the signal envelope. The louder the audio signal, the higher envelope, the greater the peak.
  • Power (Off/On)
    Power Switch :)


Mike Beigel, maker of the Mu-Tron III, made 50 of these in 1979-80.

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  • Filter Frequency Range
    Lo: 150Hz to 5KHz Resonance frequency
    Hi: 350Hz to 12KHz Resonance frequency
  • Frequency Response
    Bypass Position: 20Hz to 20KHz +/- 0.5dB
  • Dynamic Range
    105dB worst case (Measured at output)
  • Residual Noise Level
    -93dBV worst case
  • Maximum undistorted output
    +12dBV worst case
  • Maximum Input Signal Level
    Bypass Position: 6.3v RMS (+18dBV)
  • Maximum Signal Gain
    Peak Control = 10: 24dB
    Peak Control = 1: 0dB
  • Sensitivity
    (for full envelope sweep)
    Minimum: 1.8v RMS
    Maximum: 75mv RMS
  • Envelope Attack Time
    5 milliseconds to 2.5 seconds
  • Envelope Decay Time
    10 milliseconds to 5 seconds
  • Envelope Voltage Output
    0 to 10 volts
  • AC Supply Voltage
    115 VAC +/- 15%, 5 VA max
  • Fuse
    3AG 1/4 amp 125 volts


Beigel Soundlab ecf Biegel soundlabs sound labs

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