Frequency Response (Bypass Mode): Surround Processing: ±0.10 dB, 20 Hz-20 kHz for 44.1 kHz or higher input/output sample rates. At 32 kHz input and/or output sample rate, the passband is reduced to approximately 14.7 kHz. 2.0 Processing: Depending on settings, is flat or follows standard 50 µs or 75 µs pre-emphasis curve ±0.10 dB, 20 Hz-20 kHz (except at 32 kHz; see above). Output can be user-configured to be flat or pre-emphasized. (Pre-emphasis limiting allows any of the 8685's 2.0 processors to drive an analog television transmitter that uses an preemphasized FM aural carrier. This function is particularly useful when used with 2.0 processor #4, which can emit a loudness-controlled and peak-limited downmix of the surround audio. Preemphasis limiting is also useful for certain older analog studio/transmitter links.)

Noise: Output noise floor will depend upon how much gain the processor is set for (Limit Drive, AGC Drive, Two-Band Drive, and/or Multiband Drive), gating level, equalization, noise reduction, etc. The dynamic range of the A/D Converter, which has a specified overload-to-noise ratio of 110 dB, primarily governs it. The dynamic range of the digital signal processing is 144 dB.

Polarity (Bypass Mode; Operate Mode when processing chain is configured for linear phase): Absolute polarity maintained. Positive-going signal on input will result in positive-going signal on output.

Internal Processing Sample Rate: 48 kHz. We believe this provides maximum audible transparency by minimizing numerical “noise” in the equalizers and filters while still preserving a pure, transparent sound. The double-precision equalizers and crossover filters used throughout the 8685 produce at least 6 dB lower noise and nonlinear distortion than they would at 96 kHz.

Processing Resolution: Internal processing has 24 bit (fixed point) or higher resolution; uses nine Freescale (formerly Motorola) 250 MHz DSPB56724 dual-core 24-bit fixed-point DSP chips.

Delay: The minimum available input/output delay is approximately 33 ms with look-ahead limiting active and 6 ms with look-ahead limiting bypassed. This can be padded to exactly one or two frames of 24, 25, 29.97, 30, 50, 59.94, or 60 frames/second video up to a maximum delay of 60 ms. (Two frames are required for 59.94/60 fps progressively scanned video.) The HD-SDI connection provides video delay of up to 11 frames to compensate for the delay of the 8685’s loudness processing (approximately one frame), Optimix® upmixer (approximately five frames).

Surround Processing Stereo Coupling: All channels of the AGC and compressors are coupled using RMS summation. The user can select whether or not the LFE channel contributes to the RMS sum in the AGC and compressor control sidechains. Peak limiters in the multiband compressor limiter and look-ahead limiters all operate uncoupled to prevent transients in a given channel from causing audible loudness modulation in other channels. In additional, the compressors acting on the center channel can be uncoupled from the remaining channels within a user-selectable window, allowing the processing to correct the balance between dialog and remaining program elements automatically.

2.0 Processing Stereo Coupling: Stereo or dual-mono. In dual-mono mode, both processing channels have the same subjective adjustments (as determined by the active preset) but are otherwise independent, making this mode appropriate for dual-language transmissions. In stereo mode, the user can set the maximum permitted gain difference between the channels in each band of the multiband compressor/limiter. 2.0 Stereo/Dual-Mono operating mode can be set via GPI, Ethernet and serial connections, internal clock-based automation, and AES3 Status Bits.

Loudness Level Meters (x5 or x9): One set of meters for the surround processor and one set of meters for each of the 2.0 processors. In dual-mono mode, each mono channel has one set of meters. Meters can be displayed on the 8685's front-panel screen and on PC Remote software. A set of loudness meters includes a BS.1770-4 meter and a CBS meter, which are displayed side-by-side. The ITU BS.1770 meter displays Short-term and Integrated Loudness simultaneously on the same scale. The integrated loudness measurement shows the loudness of the previous 10 seconds of program material with equal time-weighting and gating per BS.1770-2. The CBS meter’s display time constants are matched to the loudness integration time of the human ear, reaching steady-state level in approximately 200 ms and having a decay time constant of approximately 300 ms. The short-term meter uses the Jones & Torick algorithm developed at CBS Technology Center. (B. L. Jones & E. L. Torick: "A New Loudness Indicator for Use in Broadcasting," J. SMPTE, September 1981, pp 772-777.)

Peak Control: As recommended in ITU-R BS.1770-4, the peak limiter is oversampled at 192 kHz, yielding a worst-case overshoot of 0.5 dB at the analog output and for all output sample rates. (To achieve this performance at 32 kHz output sample rate, it is necessary to set the 8685’s lowpass filter cutoff frequency to 15 kHz.)

Optimix™ Upmixer

Location: Built into the Optimod.

Processing Delay: 146 ms

Upmix: 2.0 to 5.0; 5.1-compatible.

Auto-detection: Defeatable auto-detection can detect stereo and surround inputs automatically and switch upmixing on when stereo material is detected.

Bass Management: Bass energy below 80 Hz is not upmixed. Any energy below 80 Hz in the left/right inputs is routed to left front/right front outputs respectively so that home receivers can perform appropriate bass management for a given setup.

Downmix Compatibility: If Delay Correction is OFF, Optimix reads the Optimod’s downmix parameters (Center and Surround downmix coefficients) from the Optimod and automatically chooses gains for the five upmixed channels that make the downmixed signals identical to Optimix's stereo inputs, assuming a Dolby Lo/Ro downmix. Optimix takes into account the settings of its Front/Rear Balance and Center Width controls. It is the user's responsibility to make sure that the Optimod's downmix level controls agree with the Center Downmix Level and Surround Downmix Level in the AC3 metadata that is being transmitted to consumers. (Per Dolby, the default value of both is -3 dB.) When Delay Correction is ON, the stereo downmix includes the effect of the center channel delay corrector, which can make the stereo downmix crisper and more intelligible than Optimix’s stereo inputs.

User Controls

Center Width determines whether extracted center-channel information will be routed solely to the center output, or if some amount of the center energy is blended into the Left Front and Right Front outputs. While setting this control to “0” maximizes the “discreteness” of the upmix, some operators prefer to mix a certain amount of center energy into Lf and Rf to ensure that dialog is not lost completely if the center channel is not correctly set up at the consumer’s receiver.

Front/Rear Balance controls the ratio between the Lf/Rf and Ls/Rs levels above 80 Hz, which determines the amount of envelopment in the upmix.

Delay Correction automatically corrects time skew or phase shift between the left and right input channels. It prevents comb filtering in the derived center channel. This maximizes mono compatibility and maintains the best possible crispness and intelligibility in the center channel, which usually contains dialog or vocals.

Mode sets Optimix to BYPASS, UPMIX, or AUTO modes.

HD-SDI Input/Output

SD-SDI (per SMPTE 259M); 1.5 Gbit/s HD-SDI (per SMPTE 292M; up to 720p and 1080i) :and 3.0 Gbit/s single-wire HD-SDI (per SMPTE 424M; 1080p). Input and output are on BNC connectors. A bypass relay is provided. Unless the bypass relay is directly connecting the HD-SDI input to the HD-SDI output (which is true when no AC power is applied to the 8685 and when it is booting up), the HD-SDI input is internally terminated with 75Ω.

Audio Channel Support: Supports only SDI audio channels 1 through 8.

Delay for A/V Sync: Includes up to 11 frames of video and metadata delay to preserve AV-sync. Core 8685 loudness control processing requires one frame of delay; the built-in Optimix® upmixer requires an additional five frame delay; Dolby-E requires one frame for decoding and one frame for encoding.

Dolby E Metadata Support: Supports Dolby-E metadata received through HD-SDI and RS485 interfaces per SMPTE RDD 06-2008. The metadata in the HD-SD stream must be embedded the HD-SDI VANC data per SMPTE 2020-2-2008 (Method-A) or SMPTE 2020-3-2008 (Method-B). Digital Audio Inputs (x4)

Configuration: Each of four hardware inputs accepts two audio channels per AES3id standard, 24 bit resolution. Internal programmable routing switcher allows any of the 10 physical input channels to be routed to the LF, RF, C, LB1, RB1, LFE, LB2, RB2, STEREO L, or STEREO R inputs of the audio processing. For the 2.0 processing, unit can detect Stereo or Two-Channel status bits appearing at Input #1 and switch the 2.0 processor between stereo and dual-mono modes. Input #4 can also be used as a sync input, accepting wordclock or AES11id sync.

User Bits: Unit can pass AES3id User Bits from Input #1 to Output #1.


Connector: BNC, female, shell bypassed to chassis via 1000 pF capacitor, EMI-suppressed. 75Ω impedance, terminated.

Input Reference Level: Variable from -30 dBFS to -10 dBFS.

Filtering: RFI filtered.

Bypass Relay: When the Optimod is powered down or booting up, each AES3id input is hard-wire bypassed to the corresponding AES3id output via a relay.

Digital Audio Outputs (x3)

Configuration: AESid. Internal, remote-controllable routing switcher allows sending LF, RF, C, LB1, RB1, LFE, LB2, RB2, STEREO L, STEREO R, DOWNMIX L, and DOWNMIX R to any hardware output channel.

Sample Rate: Internal free running at 32, 44.1, 48, 88.1 or 96 kHz, selected in software. Can also be synced to the AES3id Input #1,or to the sync input (which supports AES11id and wordclock) at 32, 44.1, 48, 88.1 or 96 kHz, as configured in software. (Passband is limited to approximately 14.7 kHz when using 32 kHz input and/or output sample rate.)

Word Length: Software selected for 24, 20, 18, or 16-bit resolution. First-order highpass noise-shaped dither can be optionally added, Dither level is automatically adjusted to complement the word length.


Output Level (100% peak modulation): -20.0 to 0.0 dBFS software controlled.

Filtering: RFI filtered.

Audio Reference Input

Configuration: Can accept wordclock or AES11id (75Ω) sync, automatically detected.

Connector: Female BNC.

Termination: Internally terminated with 75Ω

Analog Audio Outputs

Configuration: One pair of outputs, which can be configured in software to emit LF, RF, C, LB1, RB1, LFE, LB2, RB2, STEREO L, STEREO R, DOWNMIX L, DOWNMIX R, LF/RF, C, LB1/RB1, LB2/RB2, STEREO L/R, and DOWNMIX L/R signals.

Source Impedance: 50Ω, electronically balanced and floating.

Load Impedance: 600W or greater, balanced or unbalanced. Termination not required or recommended.

Output Level (100% peak modulation): Adjustable from -6 dBu to +24 dBu peak, into 600Ω or greater load, software-adjustable.

Signal-to-Noise: ≥ 100 dB unweighted (Bypass mode, 20 Hz–20 kHz bandwidth, referenced to 100% modulation).

Distortion: ≤ 0.01% THD (Bypass mode, de-emphasized) 20 Hz–20 kHz bandwidth.


D/A Conversion: 24 bit 128x oversampled.

Filtering: RFI filtered.

Audio Sync Input

Configuration: Can accept wordclock or AES11id (75Ω) sync, automatically selected.

Connector: Female BNC, shell grounded to chassis.

Termination: Internally terminated with 75Ω.

Video Sync Input

Video Sync input (per SMPTE 274M and SMPTE 296M) can be used as a reference for the output audio sample rate and to correctly align Dolby-E frames with video per Dolby's requirements (SMPTE RDD 6-2008 and Dolby Labs published specifications) in cases where HD-SDI is not in use. When HD-SDI is in use, frame sync is obtained from the HD-SDI input stream provided that the HD-SDI input complies strictly with SMPTE 299M 5.2.1 (CLK [audio clock phase data]). The video reference input is on a female BNC connector and is internally terminated with 75Ω.

Remote Computer Interface


Serial Port: 115 kbps RS-232 port DB-9 male, EMI-suppressed.

Ethernet Port: 100 Mbit/sec on RJ45 female connector.
RS-485 Serial Interface (x2)

Hardware: 115 kbps RS–485 port DB–9 male, EMI-suppressed.

Compatibility: Designed to be hardware-compatible with Dolby Digital® hardware that sends and receives Dolby Digital metadata.

Conveying and Re-authoring Dolby Metadata

The 8685 can, via an SMPTE RDD 06-2008-compliant RS-485 serial connection, via an HD-SDI connection, automatically convey its active surround metadata value to a downstream Dolby Digital encoder like the Dolby DP-569, which must be set up according to its operating instructions to receive and act upon this input. This greatly reduces the possibility that operator error will cause the wrong value of surround metadata to be transmitted to consumers.

To emit an RDD 06-2008-compliant signal, the 8685 must be receiving a valid input stream that is compliant with RDD 06-2008—this is necessary to synchronize the output metadata to video frame boundaries per the Dolby specification. When a valid input stream in present, the 8685 passes this stream unchanged to its output except for the following modifications:

  • The ac3_dialnorm word in the output metadata stream is reauthored so it is the same as the 8685's active Dialnorm value.

  • The ac3_dynrnge word in the output stream is set to 0, indicating that the downstream AC3 encoder must reauthor the line-mode DRC metadata, following the level compression profile found in the ac3_dynrng1 word in the input metadata.

  • The ac3_compre word in the output stream is set to 0, indicating that the downstream AC3 encoder must reauthor the RF-mode DRC metadata, following the level compression profile found in the ac3_compr1 word in the input metadata.

Remote Control (GPI) Interface


Voltage: 6-15V AC or DC, momentary or continuous. 12 VDC provided to facilitate use with contact closure.

Connector: DB–25 male, EMI-suppressed.

Control: User-programmable for any eight of user presets, user Setups (which contain level settings, routing switcher settings, and other such system settings), bypass, and test tone.

Filtering: RFI filtered.

Tally Outputs

Circuit Configuration: Two NPN open-collector outputs.


Current: 30 mA maximum




Voltage: 100–264 VAC, automatically selected, 50–60 Hz, 75 VA.


Configuration: Two independent power supplies with independent IEC input connectors. Power supply health is monitored and the good supply is automatically connected to the load should one supply fail.

Safety Standards: ETL listed to UL standards, CE marked.



Humidity: 0-95% RH, non-condensing.

Dimensions (W x H x D): 19” x 5.25” x 15.5” / 48.3 cm x 8.9 cm x 39.4 cm. Depth shown indicates rack penetration; overall front-to-back depth is 17.75” / 45.1 cm. Three rack units high.

Humidity: 0-95% RH, non-condensing.


Shipping Weight & Dimensions: 30 lbs / 13.6 kg - 25" x 24" x 9"


Five Years, Parts and Service: Subject to the limitations set forth in Orban's Standard Warranty Agreement.
