m908 Monitor Controller
System Specifications
m908 System Specifications Rev. G
Revision G November, 2023
M908 Monitor Controller
The Grace Design m908 Monitor Controller is designed for monitoring in 7.1, 5.1, stereo, and mono as well as higher channel count playback systems such as Dolby Atmos, Auro-3D, and DTS-X. Up to 24 channel speaker systems can be controlled. The system consists of an Audio Control Unit (ACU), Remote Control Unit (RCU), and Power Supply Unit (PSU). The RCU communicates with the ACU via RS-485 serial connection. The PSU contains dual redundant universal input power supplies which provide the ACU/RCU with DC power for analog and digital circuits.
The m908 standard features include a total of 68 digital input channels, 16 analog output channels, and 24 digital output channels. Up to 16 channels of analog inputs are available with the addition of optional 8 channel ADC modules. The Option I/O module slot provides up to 32 additional digital inputs and outputs. Up to 24 input channels can be received simultaneously and routed to the 24 channel processor. The processor has 24 output channels. The m908 supports sample rates of up to 192kHz at 24bits. Following is an outline of the m908 I/O connections.
ACU
1.1 Input Connector configuration
1.1.1 Analog
- (2) 8 Channel balanced: DB25 (optional)
- (1) 2 Channel balanced: XLR (optional)
- (1) 2 Channel unbalanced: RCA Phono (optional)
- (1) 2 Channel unbalanced RIAA phonograph preamp: RCA Phono (optional)
- (1) 1 Channel balanced Talkback microphone input w/ 48V mic power: XLR
- (1) 1 Channel balanced Talkback input: DB15 (from RCU)
1.1.2 Digital
- (3) 8 Channel AES3: DB25
- (2) 8 Channel ADAT: Optical
- (2) 2 Channel TOSLINK (Uses ADAT connectors): Optical
- (1) 2 Channel AES3: XLR
- (1) 2 Channel SPDIF: RCA Coaxial
- (1) 24 Channel USB 2.0: USB-B (asynchronous mode)
- (1) 32 Channel IO Option Module
1.2 Output connector configuration
1.2.1 Analog
- (2) 8 Channel CR Speaker balanced: DB25
- (1) 8 Channel CR Speaker/4 x 2ch Cue: DB25
- (1) 2 Channel CR Speaker balanced: XLR
- (1) 1 Channel Talkback balanced: XLR
- (2) 2 Channel Headphone: 1/4”TRS (one on RCU)
1.2.2 Digital
- (3) 8 Channel AES3 x 4: DB25
- (1) 32 Channel IO Option Module Slot
1.3 Other connectors
1.3.1 Option I/O Slot
- Dante Option
- 32 Ch In/32 Ch Out 44.1-48kHz
- 32 Ch In/32 Ch Out 88.2-96kHz
- 16ch In/16 Ch Out 176.4-192kHz
- Ravenna/AES67 (Merging ZMAN)
- 32 Ch In/32 Ch Out 44.1-192kHz
- Digilink Option
- 32 Ch In/32 Ch Out 44.1-192kHz
1.3.2 Clocking
- Connectors
- (1) Word Clock in: BNC
- (1) Word Clock through/out: BNC
- The m908 can synchronize to a variety of clock sources listed below.
- External Word Clock Input
- Internal Fixed Oscillators
- AES3 Inputs
- SPDIF Input
- ADAT Inputs
- TOSLINK Inputs
- Option I/O Module
1.3.3 Control/Computer IO
- Ethernet: RJ45 for web UI control.
- RCU: DB15 RS485/GPIO/Headphones
- USB Host: USB-A
- (3) GPIO on Pin 25 of AES3: DB25
- (1) GPIO on Pin 5 of RCU: DB15
- External Talkback switch with tally: 1/4″ TRS
RCU
2.1 I/O Connections
- Talkback/SPL Microphone, Built in
- USB Type A Host connector. User preset backup/restore via USB Mass Storage Class.
- RS485 communications and headphone signal from ACU on DB15
- Headphone Jack 1/4″ TRS
2.2 Sound Pressure Level Meter
- Sound Pressure Level with A weighting, C weighting, or no weighting.
- Peak Hold with Fast or Slow averaging
2.3 User interface
- 480×272 QVGA display, LED dimable back light with adjustable dim levels and dim timer.
- 24 detent encoder with integrated push-button for level control and parameter configuration
- 8 user defined input buttons
- 3 user defined illuminated control room speaker output buttons
- 3 x 3 speaker Solo/Mute dual color push-button array
- 3 user defined multi-function dual color push-buttons
- Illuminated talkback push button
- Illuminated DIM push-button, push-hold for headphone crossfeed on/off
- Illuminated MONO push-button, push-hold for L-R function
- Illuminated MUTE push-button
- Illuminated MON>CUE push-button
- Illuminated Setup push-button
Signal processing functions
3.1 Volume Control
3.2 Headphone cross feed
3.3 Bass Management
- Crossovers for up to 22.2 speaker systems
- Bypass available on High Pass filters
- Independent High/Low Pass filter slope settings:
- Adjustable crossover frequency.
- Adjustable LPF output trim.
3.4 Supported speaker formats
- Custom user defined formats up to 24 channels
- Atmos up to 14.2.6
- Auro-3D up to 13.1
- DTS-X up to 14.2.6
- Standard surround formats (ie: 5.1, 7.1 9.1)
- LCRS
- 2.1
- Stereo 2.0
- Mono
3.5 Downmix Formats
- 7.1 > 5.1
- 7.1 > 5.1 (Dolby PLII)
- 7.1 > LCRS
- 7.1 > LCRS2
- 7.1 > Lt/Rt
- 7.1 > Lt/Rt (Dolby PLII)
- 7.1 > Lo/Ro
- 5.1 > LCRS
- 5.1 > LCRS2
- 5.1 > Lt/Rt
- 5.1 > Lt/Rt (Dolby PLII)
- 5.1 > Lo/Ro
- LCRS > L/R
- LCRS2 > L/R
3.6 Meter Output Routing
3.7 Other
- All inputs can be routed to any available output for metering.
- Meter feed can be pre or post Input Level cal.
- Meter feed can can follow monitoring source or be fixed to a single input.
3.7.1 Inputs
- Source summing
- Up to 3 inputs can be summed together
- Sync Delay
- Level offset
- De-emphasis control
- System Clock source override
3.7.2 Speakers:
- Volume control
- MUTE/DIM
- MONO and Left minus Right
- User assignable MUTE/SOLO control
- Global level offset
- Channel level offset
- Channel Delay
- Bass management
3.7.3 Room Correction EQ
- 12 band parametric EQ per channel for Sub channels
- 12 band parametric EQ per channel for Speaker channels
3.7.4 CUE Outputs
- Up to 8 stereo cue paths
- Independent stereo level control on each cue
- Assignable talkback routing
- Source can be configured for CUE input, Control Room L/R, or downmix
3.7.5 Talkback System
- Talkback mic amp gain control for RCU and ACU talkback mics
PSU
- Talkback trigger sources:
- RCU Talkback switch
- ACU External Talkback switch
- A, B, or C User definable buttons on RCU
- GPIO 1-4 on ACU
- Each talkback trigger source can be assigned to enable a specific talkback mic (ACU and/or RCU) and route it to any or all CUE sends.
- Adjustable Talkback DIM for control room monitors
- Adjustable Talkback DIM for CUE sends
4.1 Model A140 redundant power supply
- 2 x 40W SMPS modules.
4.2 AC power input: IEC C14
4.3 DC output to ACU: CPC-8.
Signal Processing Specifications
|
SIGNAL PROCESSING |
|
| Signal Processing – Delay | |
| Input sync delay | 0-1000 ms, 5ms steps |
| Speaker channel delay | 0-250ms, 0.01ms steps |
| Signal Processing – Bass Management | |
| Crossover Frequency | 25-150Hz, 1Hz steps |
| HPF Response | 6, 12,18, 24dB/octave |
| 6dB/octave | |
| 12dB/octave | Linkwitz Riley |
| 18dB/Octave | Butterworth |
| 24dB/Octave | Linkwitz Riley |
| LPF Response | 6, 12,18, 24dB/octave |
|
SIGNAL PROCESSING |
|
| 6dB/octave | |
| 12dB/octave | Linkwitz Riley – Inverted LPF Output |
| 18dB/Octave | Butterworth |
| 24dB/Octave | Linkwitz Riley |
|
Signal Processing – Room Correction EQ |
|
| Number of bands per Channel | Up to 12 |
| Total number of bands: | 288 |
| Filter frequency range, 246 steps ~1/24 octave spacing | 10-20,000Hz |
| Peak Filter Q | 0.02-50 |
| Shelf Filter Slope “S” | 0.02-10 |
| Filter Shapes | Low Shelf, Low Pass, Peak, High Pass, High Shelf |
|
Monitor Control |
|
| Attenuation Range | -inf, -99.5dB to 0dB, 0.5dB steps |
| DIM Attenuation | -30.0dB to 0.0dB, 0.5dB steps |
| MONO Sum Law | -9.0dB to 0dB, 0.5dB steps |
|
Speaker System Latency AD in to DA out |
|
| Fs=44.1kHz | 5.1ms |
| Fs=48kHz | 4.7ms |
| Fs=88.2kHz | 2.6ms |
| Fs=96kHz | 2.4ms |
| Fs=176.4kHz | 1.3ms |
| Fs=192kHz | 1.2ms |
|
Cue System Latency AD in to DA out |
|
| Fs=44.1kHz | 0.70ms |
| Fs=48kHz | 0.64ms |
| Fs=88.2kHz | 0.35ms |
| Fs=96kHz | 0.32ms |
| Fs=176.4kHz | 0.15ms |
| Fs=192kHz | 0.14ms |
Electrical Specifications
|
DA CONVERTER CONTROL ROOM OUTPUTS Fs=48kHz unless otherwise noted. |
||
| THD+N | ||
| 0dBFS In, +18dBu Out, 22Hz-22kHz BW | <-115dB | |
| Intermodulation Distortion | ||
| SMTPE/DIN 4:1 50Hz, 7kHz, 1.0V Out | <107dB | |
| Frequency response | +/-0.2dB | -3dB |
| 44.1kHz Fs | DC-20.5kHz | DC-20.6kHz |
|
DA CONVERTER CONTROL ROOM OUTPUTS Fs=48kHz unless otherwise noted. |
||
| 48kHz Fs | DC-22.2kHz | DC-23.5kHz |
| 88.2kHz Fs | DC-27kHz | DC-43.2kHz |
| 96kHz Fs | DC-27kHz | DC-47kHz |
| 176.4kHz Fs | DC-27kHz | DC-85.5kHz |
| 192kHz Fs | DC-27kHz | DC-92.7kHz |
| Dynamic Range | ||
| 20-22kHz bandwidth | 123dB | |
| 20-22kHz bandwidth and A weighting filter | 125dB | |
| Output Level | ||
| 0dBFS | +18dBu | |
| Output Noise | ||
| 20-22kHz | -105dBu | |
| 2022kHz, A weighting filter | -107dBu | |
| Crosstalk | ||
| Interchannel crosstalk, 1kHz | -123dB | |
| Interchannel crosstalk, 10kHz | -103dB | |
| Attenuation Range | 0 to -99dB, 0.5dB steps | |
| Channel Tracking Accuracy | +/-0.05dB | |
| Maximum Output Level | +18dBu | |
| Output Impedance (balanced) | 300Ω | |
A/D CONVERTER OPTION Fs=48kHz unless otherwise noted.
| THD+N | ||
| 1kHz, -1dBFS, 20Hz-22kHz | < 0.0004% | |
| Intermodulation Distortion | ||
| IMD SMPTE 4:1 60Hz, 7kHz, -3dBFS | <0.002% | |
| Frequency response | +/-0.2dB | -3dB |
| 44.1kHz Fs | 14Hz-20.6kHz | 4.5Hz-21.1kHz |
| 48kHz Fs | 15Hz-22.4kHz | 4.5Hz-23.0kHz |
| 88.2kHz Fs | 14.9Hz-41.1kHz | 4.5Hz-42.3kHz |
| 96kHz Fs | 15Hz-44.7kHz | 4.5Hz-46.1kHz |
| 176.4kHz Fs | 15.5Hz-79.6kHz | 4.5Hz-88.09kHz |
| 192kHz Fs | 15Hz-86.7kHz | 4.5Hz-95.97kHz |
| Dynamic range | ||
| 22Hz-24kHz, 48kHz | >117dB | |
| “A” weighted, 48kHz | >120dB | |
| Full scale input level 0dBFS | ||
| Jumper Selectable | +20dBu OR +24dBu | |
| Crosstalk | ||
A/D CONVERTER OPTION Fs=48kHz unless otherwise noted.
| Interchannel crosstalk, 1kHz | -140dB |
| Interchannel crosstalk, 10kHz | -127dB |
| Input Impedance | |
| Balanced Input (DB25 or XLR) | 20k Ω |
| Unbalanced Input | 10k Ω |
TALKBACK MIC IN > TALKBACK MIC OUT (ANALOG)
| Gain Range | +11, +19-74dB in 1dB steps |
| Frequency Response | |
| @ 40dB gain ± 0.2dB (50Ω source) | 15Hz-300kHz |
| @ 40dB gain ± 3dB (50Ω source) | 4.5Hz-1.0MHz |
| THD+N | |
| @ 20dB gain +20dBu out, 1kHz | <.0003% |
| @ 40dB gain +20dBu out, 1kHz | <.0010% |
| @ 60dB gain +20dBu out, 1kHz | <.0080% |
| Intermodulation Distortion | |
| @ 40dB gain +20dBu out | |
| SMPTE/DIN 1:1 (50Hz, 7kHz) | <.001% |
| SMPTE/DIN 4:1 (50Hz, 7kHz) | <.0020% |
| Noise – Referred to Input | |
| @ 60dB gain, 50Ω source | -129dB |
| @ 60dB gain, 150Ω source | -127dB |
| @ 60dB gain, 600Ω source | -123dB |
| Phase Deviation | |
| 40-20KHz @ 40dB gain | <5° |
| Crosstalk | |
| Any Channel @ 40dB gain 1kHz | -127dB |
| Any Channel @ 40dB gain 10kHz | -113dB |
| CMRR | |
| @ 60dB gain, +20dBu CM, 1kHz | >75dB |
| @ 60dB gain, +20dBu CM, 10kHz | >85dB |
| @ 60dB gain, +20dBu CM, 60Hz | >55dB |
| Maximum Output Level | |
| Balanced, 1kHz, 100kΩ Load | +27dBu |
| Balanced, 1kHz, 600Ω Load | +26.2dBu |
| Impedance | |
| Input | 8kΩ |
| Output | 300Ω |
HEADPHONE AMPLIFIER
| THD+N | |||
| +10dBu Out, 22Hz-22kHz BW | <0.0009% | ||
| +10dBu Out, 22Hz-22kHz BW, 20Ω load(300mW) | <0.030% | ||
| Intermodulation Distortion | |||
| SMTPE/DIN 4:1 50Hz, 7kHz, 10dBu out, no load | <0.0015% | ||
| SMTPE/DIN 4:1 50Hz, 7kHz, 10dBu out, 20Ω load (300mW) | <0.060% | ||
| Frequency response | |||
| Fs=192kHz , ±3dB | 0.2Hz-92kHz | ||
| Fs=192kHz , ±0.2dB | 1Hz-27kHz | ||
| Dynamic Range | |||
| 20-22kHz bandwidth | >114dB | ||
| 20-22kHz bandwidth and A weighting filter | >118dB | ||
| Output Noise | |||
| 20-22kHz | < -93dBu | ||
| 20-22kHz, A weighting filter | < -97dBu | ||
| Crosstalk | |||
| Interchannel crosstalk, 1kHz | < -107dB | ||
| Interchannel crosstalk, 1kHz | < -98dB | ||
| Channel Matching Accuracy | |||
| +/-0.05dB | |||
| Maximum Output Level, Both Channels Driven | Level | Power | |
| 100K Ω load | +21.0dBu | NA | |
| 20 Ω load | +16.4dBu | 1.3W | |
| 32 Ω load | +19.2dBu | 1.57W | |
| 600 Ω load | +21.4dBu | 280mW | |
| Headphone Output Impedance | 1.3Ω | ||
RIAA PHONO AMPLIFIER OPTION
| GAIN | ||
| LOW GAIN | HIGH GAIN | |
| Gain @1kHz | 40dB | 60dB |
| Noise | ||
| 22Hz-22kHz | -90dBu | -71dBu |
| 22-22kHz, A weighting filter | -96dBu | -76dBu |
| THD+N | ||
| 1kHz, 5mV IN | <0.0080% | |
| 1kHz, 1mV IN | <0.040% | |
| SMPTE/DIN Intermodulation Distortion | ||
| SMPTE/DIN 4:1 100/2kHz, 5mV IN | <0.004% | |
| SMPTE/DIN 4:1 100/2kHz, 1mV IN | <0.03% | |
| Max Input Level | ||
| 0.1% THD+N | 110mV | 10mV |
| Sub Sonic Filter | ||
| -3dB | 12Hz | 12Hz |
| RIAA EQ | ||
| accuracy | ±0.10dB | ±0.10dB |
GPIO
| GPIO Inputs | +5V | +3.3V |
| Input High Voltage level | >3.3V | >2.0V |
| Input Low Voltage level | <1.5V | <0.8V |
| Max Input Voltage level | 5.5V | 3.8V |
| GPIO Outputs | +5V | +3.3V |
| Output High Voltage | 5.0V | 3.3V |
| Max Output Current | 15mA | 10mA |
| Note: GPIO outputs have 330Ω series output resistors. | ||
| External ACU Talkback switch input | ||
| Switch input pull-up voltage | 3.3V | |
| Switch input pull-up resistance | 10KΩ | |
| Tally output voltage | 5.0V | |
| Tally output resistance | 330Ω | |
CLOCKING
| Supported Sample Rates kHz | 44.1, 48, 88.2, 96, 176.4, 192 |
| External Clock | |
| Lock Range | FS +/- 1% |
| Word Clock Input Voltage (BNC) | 200mV-5.0V peak to peak |
| Word Clock Output voltage | 5V peak to peak |
| Word Clock Input Impedance | 48kΩ or 75Ω |
| Word Clock polarity | Left data: High, Right data: Low |
| Intrinsic Jitter, 10Hz-20kHz BW | |
| Internal Clock | <40ps RMS |
| External Clock | <40ps RMS |
| Jitter Rejection Corner Frequency | 0.5Hz |
GENERAL
|
|
Weight |
Dimensions |
| Audio Control Unit | 6.8lbs (3.2kg) | 19″W x 3.5″ H x 10.9″ L |
| Remote Control Unit | 2.2lbs (1.0kg) | 10.5″ W x 2.5″ H x 5.1″ L |
| Power Supply Unit | 2.6lbs (1.2kg) | 8.5″ W x 1.7″ H x 8.2″ L |
| Power Consumption | ||
| 90-250V~ 50-60Hz | 50W Max | |
Mechanical Specifications
7.1 Dimensions
7.1.1 [ACU dimensions drawing]
7.1.2 [RCU dimensions drawing]
7.1.3 [PSU dimensions drawing]
7.2 Document Revisions
|
Rev. |
Description | Date |
Initials |
| A | Initial preliminary release | 05/20/19 | MBG |
| B | Correct Ext. Talkback mic gain range Correct firmware version | 10/21/19 | MBG |
| C | Correct ADC Input sensitivity | 10/24/19 | MBG |
| D | Update Room EQ Q range Update System and Cue Latency specifications |
10/28/19 | MBG |
| E | Update power consumption specification | 11/13/19 | MBG |
| F | Add Wordclock Polarity specification Updated specifications for 1.0.7 Firmware Removed Ross Bach Liberty option | 03/25/21 | MBG |
| G | Updated Dante channel count for 64ch Brooklyn module. Updated number of EQ bands per channel to 12. Updated speaker delay increment to 0.01ms. Updated crossover frequency range. Added high and low shelf slope parameter and range. | 11/17/23 | MBG |
Documents / Resources
 |
GRACE DESIGN M908 Monitor Controller [pdf] Instruction Manual M908 Monitor Controller, M908, Monitor Controller, Controller |