715 - DAVID FM Stereo Processor/Generator

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With the Introduction of the Model 715, the "DAVID", Inovonics has reduced the combined functions of stereo audio processing and FM-stereo "multiplex" signal generation to the most basic level.


  • Stereo audio processing includes slow, "Gan riding" AGC, Dynam,ic Compression, Peak and independent High Frequency Limiting, and a single-knob control for adjusting Program Density.

  • Extended-response low-pass filtering with proprietary overshoot compensation to ensure full carrier modulation without need for composite clipping.

  • Digital Synthesis of pilot and subcarrier for unexcelled performance and freedom from drift and routine adjustment.

  • Built-in combining for SCA or RDS subcarriers, including an independent 19kHz, TTL-level Stereo Pilot output for RDS sync.



Frequency Response

(through appropriate deemphasis network)  ±1dB, 20 Hz - 16kHz; -60dB or better at 19kHz.

Stereo Separation

<60dB, 20Hz - 16kHz


<0.5%THD in demodulated audio above 200Hz.  Distortion below 200Hz is a function of the PROCESSING DENSITY control setting.


Better than 80dB below 100% modulation in demodulated audio 20Hz - 16kHz. 38kHz residual and “digital” noise above 54kHz, -75dB or better.

Crosstalk (M/S or S/M)

–55dB or better “nonlinear” crosstalk at TEST INPUTS (processing bypassed),  -45dB or better overall.

Stereo Pilot

19kHz, ±1Hz; adjustable between 6% and 12% relative to 100% modulation. Pilot distortion <0.5%THD.

Program Inputs

LINE INPUTS for Left and Right Channel program are active-balanced / bridging, and accept nominal line levels between  –15dBu and +15dBu.

Test Inputs

Unbalanced TEST INPUTS bypass audio processing and preemphasis circuitry for direct signal feed to Stereo Generator section. 0dBu input gives 100% modulation.

SCA / RDS Input

Unbalanced input accommodates SCA or RDS sub-carrier signal levels between –20dBu and 0dBu for nominal 5-10% injection.


Integral to split-spectrum audio processing circuitry and non-defeatable.  May be jumpered for >75µs or 50µs characteristic.TEST INPUTS bypass processing and give a “flat” output.

AGC Amplifier

Slow (0.5dB/sec.) correction for long term input level variations;  ±10dB capture range displayed by LED indicators.


Fast-acting peak limiter has secondary “platform” time constant to compress dynamic range with average-value weighting.  Independent high frequency limiter conforms to selected preemphasis characteristic. LEDs indicate peak and H.F. limiter action and compressor gain state.  DENSITY control alters time constants and platform values.

Signal Clipping

Program signal clipping is relegated to non-repetitive limiter overshoots 1 ms or less in duration. “Safety” clipping of the Composite Output signal is performed prior ro Stereo Pilot insertion.

Composite Output

Single-ended (unbalanced), “zero” (voltage source) impedance.  Level is adjustable between -5dBu and +12dBu (0.5 to 3V r.m.s. or 1.2 tp 8V p-p).

19kHz Sync Output

TTL-level symmetrical squareware, in phase with 19kHz Stereo Pilot component in Composite Output signal.

Digital Synthesis Sampling Rate

608kHz (16X subcarrier oversampling)

Power Requirements

105-130VAC or 210-255VAC, 50/60Hz; 15W

Size and Weight

1- 3/4” H x 19” W x 7” D (1U); 7 lbs.

Patent Notice

Low-pass filter overshoot compensation circuitry employed in the Model 715 is protected under U.S. Patent No. 4,737,725.