FM Multiplex Decoder

Share on Facebook Share on Twitter

Inovonics’ INOmini 514 is a standalone decoder for FM-stereo multiplex signals. It accepts a demodulated FM-baseband input and decodes the signal to discrete left and right channel audio. The recovered stereo program is available as a professional line-level balanced output, and also as an AES digital audio signal.

Local alarm ‘tallies’ and selectable de-emphasis curves make the INOmini 514 an essential tool for professional applications wherever a stereo-baseband signal needs to be decoded and monitored.


  • Decodes Composite/MPX signal into L/R audio

  • Analog L/R and AES-digital program line outputs

  • Accurate front-panel metering

  • Front-panel alarms with rear-panel ‘tallies’ for program Audio Loss (silence sense) and stereo Pilot Loss (stereo/mono status)

  • Conforms to the worldwide FM ‘pilot-tone’ system; selectable 75μs/50μs de-emphasis



Multiplex (MPX) Input

Unbalanced/bridging (BNC); 10k input impedance; requires 0.5V p-p minimum signal.

L/R Analog Line Outputs

Active-balanced (XLR), 200-ohm source impedance; +4dBu output at ‘0dB’ on front-panel meter.

AES Digital Output

Transformer-balanced (XLR), 44.1kHz sampling rate; –6dBFS output at ‘0dB’ on front-panel meter.

Headphone Jack

3.5mm (TRS) for low-Z or high-Z phones; fixed listening level

Program Audio De-Emphasis

75μs/50μs, selected with push-on jumpers under the top cover

Forced-Mono Operation

Enabled with a push-on jumper under the top cover

Audio Frequency Response

Follows selected de-emphasis characteristic ±0.5dB, 20Hz to 15kHz

Noise (Unweighted SNR re: ±75kHz deviation)

  • MONO: ≥72dB; analog/digital
  • STEREO: ≥70dB; analog/digital


≤0.05% THD, 20Hz to 15kHz (analog/digital)

Stereo Separation

50dB 20Hz to 15kHz (analog/digital)

Alarm Tallies

Individual open-collector NPN transistor outputs for Program Audio Loss (either/both channels) and Pilot Loss (stereo/mono indicator)

Power Requirement

12VDC at 230mA. A ‘wall-outlet transformer’ (WallWart®) switching-type power supply appropriate to the destination AC mains voltage is provided.

Mounting Options

An optional rack adapter accepts up to three INOmini modules in a 1U, 19-inch rack space. Alternatively the 514 may easily be fastened to any convenient surface with two small screws.

Size and Weight

1.6”H x 5.5”W x 5.5”D; 4 lbs. shipping weight.


Continuous operation at ambient temperatures between 32ºF/0ºC and 122ºF/50ºC; 0-95% relative humidity, non-condensing, altitudes to 10,000ft/3,048m.