FM-531 HD

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FM-531 HD

Our FM-531HD on-air FM processor has everything our flagship AirAura processor has for squeaky-clean audio and bass that rocks, but in a 1RU package and at a very budget-friendly price.

Our  FM-531HD is a 1RU on-air processor for FM/HD use. Packaged in a compact, 1RU form factor, this new processor brings the multiband precision of our flagship AirAura processor to a budget-friendly price point. Its Vorsis Ultra High Resolution processing technology delivers superb on-air sound that’s loud, yet detailed.

Features include a distortion-managed final clipper for squeaky-clean audio, smart stereo enhancement, bass management for deep, yet clean bass, and Sweet Spot Technology for consistent sound regardless of density variations in the source material.


Distortion-Managed Final Clipper

The technology utilized in our new FM-531HD final peak clipper does not generate the objectionable aliasing and intermodulation distortions commonly associated with less-complex clipper technology.

Similar in certain ways to our acclaimed 31-band 'Fine Grain' limiter (a Vorsis exclusive), the FM-531HD utilizes high resolution distortion recognition algorithms to discern audio from distortion. The fine-grained selectivity afforded by this technology is the best way to sense and truly mitigate distortion. Other technologies can only make a "best guess" at separating desirable audio components from undesirable distortion products.

By analyzing the audio and the distortion products created during peak control, the FM-531HD removes distortion products and other artifacts that a listener might find objectionable. It is highly adept at minimizing intermodulation distortion, especially close-spaced difference frequency intermodulation products in the midrange frequencies where human hearing is the most sensitive.


“Full Detail” Processing

"Full Detail" processing overcomes the limitations of peak limiters in other on-air processors. Using 31 limiter bands selected according to ISO standard 1/3 octave center frequencies the FM-531HD limiters (one for FM, one for HD) perform precision spectral energy control without generating additional density or artifacts usually associated with peak limiters having fewer bands. Operating according to accepted principles of human psychoacoustics, the action of the Stealth Limiter™ goes completely unnoticed by the ear. Because of the need for very shallow limiting in each band, there are absolutely no 'swishing' artifacts and no unnatural density buildup; just increased on-air loudness, detail, and "listenability" of the station's programming.


Sweet Spot Technology

Sweet Spot Technology (SST) has been designed by Vorsis to manage the behavior of the multiband AGC as program content density changes, something a typical broadband AGC simply cannot do. It effortlessly handles transitions between the hyper-compressed recordings of today and those of the past that have considerably more dynamic range. SST achieves uncannily natural-sounding consistency in both on-air loudness and spectral balance regardless of density variations in the incoming source material.


Vorsis Bass Management System - v2.0

The Vorsis Bass Management System (VBMS) enhances deep bass and impact without affecting the cleanliness of mid and high frequency program. Bass detail and the clarity of higher frequency audio are enhanced by this powerful, innovative algorithm. With VBMS’ ‘Texture’ and new ‘Sub’ controls, on-air bass has never sounded sogood and so deep and natural.


Exclusive Multipath Limiter

Exclusive to the Wheatstone line of audio processors is the Multipath Limiter. This single user control can help mitigate the audible effects of multipath as well as reduce receiver-induced stereo blend by limiting the amount of L-R as a percentage of L+R for a more consistent and predictable sound.


Smart Stereo Enhancement

Stereo enhancement is a standard feature on all Vorsis on-air processors and utilizes a new Vorsis technology: Smart Stereo Enhancement. Operating in the sum and difference domain and utilizing specialized spectral management algorithms, it provides a smooth, natural, wide listening experience without triggering multipath effects. It delivers an extremely stable 'on-air' stereo image that's exciting to listen to. Users have reported hearing, for the very first time, artistically important nuances in familiar music that could not be heard when that material was processed by other on-air processors.


WheatNet-IP Compatibility

The FM-531HD is fully compatible with the WheatNet-IP Intelligent Network. 


Wheatstone® baseband192

Wheatstone’s baseband192 is an open standard technology that eliminates the use of an analog composite interface between processing and transmission, which has been the last holdout to the 100% digital air chain. 
A single AES/EBU cable between a Wheatstone processor and a current solid-state FM transmitter carries the baseband signal, bypassing the need 
for multiplexing in the exciter and eliminating the resulting signal overshoot with associated loudness tradeoff. The baseband192 interface is now available as a standard feature in Wheatstone AirAura X3, FM-531HD and VP-8IP audio processors.
See more at:  Wheatstone Audio Processing Technology Overview

  • Distortion-managed final clipper for squeaky clean audio
  • 31-band limiting for precision spectral energy control without generating additional artifacts typically associated fewer bands
  • Exclusive SST technology for sound consistency regardless of density variations in the incoming source material
  • Bass management technology for deep bass without affecting the cleanliness of mid and high frequency program
  • Exclusive Multipath Limiter for mitigating the effects of multipath
  • Smart stereo enhancement for extremely stable ‘on-air’ stereo image that’s exciting to listen to
  • Audio Guru ™ GUI included standard
  • Four band phase linear adjustable crossover feeding a four band AGC
  • Four band phase linear crossover feeding a four band limiter
  • Exclusive VBMS™ (Vorsis Bass Management System)  
  • FM peak control via oversampled lookahead limiter or distortion masked clipper
  • Four band full parametric equalizer
  • Variable high pass filter and voice phase rotator
  • AES3 digital input accepts 32kHz - 96kHz
  • AES3 digital output automatically synchronizes to AES3 digital input
  • Wheatstone® baseband192 built in for digital link to transmitter
    See more at:  Wheatstone Audio Processing Technology Overview


Headroom 20dB

Nominal Operating Level -20dBFS digital, +4dBu analog

Latency (FM Section) 15.4ms, analog in to analog out, 14.2ms, AES in to AES out

Latency (HD/DAB Section) 11.2ms, analog in to analog out, 12.6ms, AES in to AES out



Type electronic differential, RFI suppressed

Input Impedance >10K ohm (bridging)

Optimum Source Impedance <1k ohm="" p="">



Data Standard: AES3 (AES/EBU), two channel stereo



Data Standard: AES3 (AES/EBU), two channel stereo



Transmitter link (baseband 192)



Data Standard: WheatNet-IP, two-channel stereo.



Automatic failover to alternate audio input source if audio fails on primary input.



Makes voice waveforms more symmetrical to reduce processing distortion.



Three separate four-band parametric equalizers:

EQ Set 1: pre or post 5-band AGC

EQ Set 2: post HD/DAB multi-band limiter

EQ Set 3: post FM multiband limiter



AGC operates in sum/difference domain.

Exclusive Vorsis SST retunes the five band AGC/Compressor to maintain 

consistent program density as programming elements change.



One 31-band section is assigned to FM signal path

One 31-band section is assigned to HD signal path

FM section operating modes: Independent, Wide, and Timbral



VBMS-II intelligently minimizes bass induced intermodulation distortion and improves bass impact. ‘VBMS Texture’ control also permits fine tuning of how deep bass sounds on smaller loudspeakers. Bass Tools adds virtual subwoofer capabilities, extending a floor feel by intelligently enhancing frequencies in the 40-90Hz range.



Advanced ‘distortion aware’ final peak controller intelligently manages processing artifacts to minimize or even eliminate audible processing and intermodulation distortion.



Stereo Width Limiter to automatically minimize multipath distortion

Dual SCA/RDS/RBDS Inputs

Dual Composite Multiplex outputs



Automatically changes presets daily, weekly, or as desired, including long-form ‘once in the future’ preset changes.



Responds to commands from program automation system via Ethernet connectivity. Commands from program automation can change presets or even modify individual processing adjustments without changing presets.



Remote control is by dedicated Windows-based Graphical User Interface with connectivity via 100BaseT wired Ethernet.



Eight optoisolated logic inputs are slaved to first eight preset storage locations.



90-240VAC, 50-60Hz, <100VA



19” wide, 1.75” high, 13.75” deep (16” with connectors)



16 lbs



Operating Manual, Windows-based Audio Processing Guru® Control Software, 6’ IEC power cable, CDROM containing manual in PDF form, Factory Default Preset Library. 

GUI Pro Software, which allows unlimited access to every processing parameter, is available as a free download at



Wheatstone Processing Videos

In January 2017, Mike Erickson sat down with Scott Fybush to talk all things processing. We shot video of the conversations and got some exceptional stuff. Learn about what it takes to provide modern, airwave-dominating clean sound that listeners rave about.

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