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AKG DFM 4 x 4

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Digital Four Channel Signal Processor with Feedback Eliminator


The DFM 4x4 is a sophisticated DSP based multichannel audio signal-processing device. Based on a state-of-the-art 32- bit floating-point digital signal processor, internal calculations are carried out with greater than 120 dB dynamic range. 24-bit A/D and D/A conversion guarantees superior audio signal quality.

The DFM 4x4 implements an Automatic Digital Feedback Eliminator (ADFE) on each channel. Feedback frequencies are quickly located in real time and a narrow notch filter is placed on the offending frequency. This immediately restores audio system stability.

The DFM 4x4 includes a 4x4 input matrix to allow complete flexibility in signal routing. Each crosspoint may be adjusted with gains ranging from +10 dB to -20 dB, plus off. Input gain control before the matrix can be adjusted from +10 dB to -68 dB plus off. The input gain can also be controlled via the programmable logic inputs or through RS-232 serial commands.

Up to 12 filters are available for each channel. The user can select how many of the 12 filters that the ADFE will use and how many will be used for other signal processing. The user adjustable filters can be highpass, lowpass, shelving, and fully parametric EQ. Each channel includes both a full-function compressor for dynamic range control, and a limiter for maximum signal control. The compressor features adjustable attack and release times, threshold, and a choice of useful compression ratios. The limiter allows adjustment of attack and release times and limiting threshold.

An audio delay per output rounds out the signal processing available on the DFM 4x4. Up to 182 mS of audio delay may be applied to each channel in 20.83 uS increments.

The addition of programmable logic inputs and outputs allows complex control of the DFM 4x4 to be implemented easily. Programmable inputs can mute and unmute inputs and outputs, allow input and output levels to be controlled continuously via potentiometers or control voltages, or recall memory presets. Programmable outputs can be used to indicate the current state of programmable inputs, for example indicating whether a channel is muted or unmuted. Full control of all aspects of DFM 4x4 operation is available through the LecNetTM RS-232 serial port.

The basic model is a 19" rack mount assembly with a single 4 in 4 out processor. Each input can be routed to any one or more output channels. The ADFE (automatic digital feedback eliminator), all filters and processing can be applied independently to each output channel.

Multiple processors can be mounted in a rack and powered by individual power supplies, with serial communications looped through the EXPANSION ports to the other processors or LecNetTM devices.

The gain for each input is individually controlled. Following the input gain control is a 4x4 matrix with fully adjustable crosspoint gains. Each of the four matrix outputs has a complement of 12 user-adjustable filters, a full function compressor, a limiter, audio delay, and individual output gain control.

13 programmable inputs and 8 programmable outputs allow sophisticated control of almost every aspect of the DF M4x4. Programmable inputs provide input and output level control or muting, as well as the recall of any of the 8 available preset memories. Programmable outputs can indicate the state of programmable inputs. For example, a programmable output can be used to light an LED as an indication of whether an output is muted or unmuted.


  • 4 in 4 out DSP based audio signal processor

  • Automatic Digital Feedback Eliminator (ADFE) on each channel

  • Complete 4x4 matrix on the input

  • Up to 12 user adjustable filters on each channel

  • Compressor with user adjustable attack, release, threshold and compression ratio on each channel

  • Limiter with user adjustable attack, release, and threshold on each channel

  • 182mS of audio delay (with 20.83uS increments) on each channel

  • Full input and output level control, with front panel input level metering

  • Programmable logic inputs and outputs for complete system control

  • 8 nonvolatile preset memories

  • RS-232 serial port for control by PC, AMX, or CrestronTM


  • Connectors:Audio: 5-pin Phoenix styleExp In/Out: 8-pin mini DINProgrammable I/O: 15 pin D-SubLecNet RS-232: 3.5mm Stereo jack

  • Audio Inputs:Type: Electronically balanced and RF filteredImpedance: 40K Ohms balanced input impedance, 40K Ohms unbalanced input impedance

  • Max Input Level: +20dBu

  • Gain Range: +10dB to -68dB, plus off

  • Audio Outputs:Type: Electronically balanced and RF filteredImpedance: 200 Ohms balanced, 100 Ohms unbalanced

  • Max Output Level: +20dBu

  • Gain Range: 0dB to -78dB, plus off

  • Matrix Crosspoints: Gain Setting: +10dB to -20dB, plus off in 1dB increments

  • User Defined Filters:1st and 2nd order lowpass and highpass1st and 2nd order shelving fully parametric EQ; +/- 15 dB

  • Feedback Eliminator (ADFE):Filter Type: 1/5 octave notch, placed with 1/10 octave accuracyFilter Cut: -6dB, -12dB

  • Compressor:Attack Time: 0.5mS to 128mS in 0.5mS incrementsRelease Time: 10mS to 2.55S in 10mS incrementThreshold: +20dBu to -40dBu in 1dB incrementsCompression Ratio: 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1

  • Limiter:Attack Time: 0.125mS to 32mS in .125mS incrementsRelease Time: 2mS to 512S in 2mS incrementsThreshold: +20dBu to -40dBu in 1dB increments

  • Digital Delay: Max. 182mS, in 20.83uS increments

  • Programmable Inputs/Outputs:Input Voltage Range: 0VDC - +5VDCAnalog Control: 0dB to -30dB plus off control range, 156mV/dB control sensitivityLogic Control: Active LowProgrammable Output: Active Low, 100mA max. current 40VDC maximum voltage.

  • Serial Communication: RS-232, 9600 baud, 8 data bits, no parity, 1 stop bit

  • Default LecNet Address: 143

  • Frequency Response: 20Hz - 20kHz, +/- 1dB

  • System THD: Less than .05%

  • System IMD: Less than .05%

  • System Dynamic Range: 100dB

  • Power Consumption: 10 Watts max at 20VAC

  • Dimensions: 19" wide x 1.75" high x 8" deep

Q & A

DFM 4 x 4
MFR Part Number
DFM 4 X 4
Product Category
Unit of Measure
Shipping Weight
7.00 lbs.
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