Optimod FM/HD 8600Si
Optimod-FM 8600 was a hit as soon as it was introduced. Compared to Orban’s previous flagship, the 8600’s dramatically improved “MX” peak limiter technology decreased distortion while increasing transient punch and high frequency power handling capacity. A significant number of broadcasters have asked us to make the 8600’s sound available in a compact package at a lower price. Orban’s response is the 8600Si, which offers 8600-class sound in a single rack unit. An efficient, switching power supply ensures that the 8600Si runs cool even in a crowded rack. The 8600Si includes simultaneous processing for FM and for digital transmissions like netcasts, DAB+ and HD Radio.
The 8600Si provides stereo enhancement, equalization, AGC, multiband compression, low-IM peak limiting, stereo encoding, and composite limiting — everything that even the most competitive major market station needs to stand out on the dial. More than 20 excellent sounding, format specific factory presets get you started. You’ll find all of your favorite 8500 presets, plus the 8600 “MX” presets designed by Bob Orban and Greg Ogonowski to exploit the exciting possibilities inherent in the 8600Si’s peak limiter technology. Although the factory presets are fully competent “out of the box”. You can customize them with easy one-knob LESS-MORE control. Full Control gives you the versatility to customize your audio further. Orban’s Quick setup, which is a guided sequence of screens through the 8600Si‘s setup, is the easiest way to have your station On Air quickly.
Improved Peak Limiter Technology
Dramatically improved peak limiter technology decreases distortion while increasing transient punch and high frequency power handling capacity. Compared to the FM-channel peak limiter in OPTIMOD-FM 8500, the new peak limiter typically provides 2.5 to 3 dB more power at high frequencies, which minimizes audible HF loss caused by pre-emphasis limiting. Drums and percussion cut through the mix. Highs are airy. “Problem material” that used to cause audible distortion is handled cleanly.
While this design offers about the same loudness as 8500 processing, its main goal is to make FM analog broadcasts more competitive with the cleanliness, punch, and open high frequencies of the digital media against which FM analog transmissions now battle. The FM loudness wars represent 20th-century thinking; in the 21st century, the new competition is digital media. Thanks to its fresh, crisp sound, the 8600Si helps level the playing field between analog FM and its ever more aggressive digital-only competitors.
For Digital Radio broadcasters who prefer using a separate processor for the digital channel, the 8600Si’s built-in delay (up to 16 seconds) in the analog processing path vastly improves installation versatility in HD Radio facilities, freeing you from the need to use the delay line built into the Digital Radio exciter. This allows you to use the 8600Si’s built-in stereo encoder and composite limiter to drive the analog FM transmitter, ensuring no-compromise analog-channel loudness.
The 8600Si’ HD (“Digital Radio”) output is designed to feed streaming, netcasting, and digital satellite or cable radio channels, which can be Eureka 147, DRM, DAB + or the iBiquity® HD Radio system (formerly known as “IBOC”—“In-Band On-Channel”) approved for use in the United States. The equalizer and five-band compressor/limiter in the digital processing chain have their own sets of user-adjustable audio controls that are independent of the controls in the FM analog transmission chain’s equalizer and five-band compressor/limiter. The bottom line? Processing that optimizes the sound of your FM channel while punching remarkably crisp, clean, CD-like audio through to your digital channel audience.
Loudness and True Peak control
The digital radio and analog radio processing chains offer ITU-R BS.1770-3+ Loudness Meters and Safety Limiters for use in countries that enforce a BS.1770 loudness limit on digital and/or analog radio broadcasts. The 8600Si implements “true peak control” in the HD processing chain by oversampling the HD peak limiter’s sidechain at 256 kHz. This allows the 8600Si to prevent clipping in a playback device’s analog signal path by predicting and controlling the analog peak level follow the playback device’s reconstruction filter to an accuracy of better than 0.5 dB. For typical program material, accuracy is 0.2 dB. Without true peak control, analog clipping can occur even if all peak values of the digital samples are below 0 dBFS. This phenomenon has also been termed “0 dBFS+.” Thanks to true peak control, sample rate conversion, unless it removes high frequency program energy or introduces group delay distortion, cannot cause sample peaks to increase more than 0.5 dB.
Versatility doesn’t stop with sound.
The 8600Si has an internal, DSP-based stereo encoder (with a patented “half- cosine interpolation” composite limiter operating at 512 kHz sample rate) to generate the pilot tone stereo baseband signal and control its peak level. The composite limiter is a unique, “you can only do this in DSP” process that beats composite clippers by preserving stereo imaging while fully protecting the stereo pilot tone, RDS/RBDS, and subcarriers. For our European customers, a second generation ITU BS 412 multiplex power controller yields the best possible coverage while flawlessly complying with the standard. You can adjust it to maximize loudness within the constraints of the BS 412 standard or to produce less gain change at the expense of slightly lower loudness. The 8600Si has the ability to apply MPX power gain reduction after the clippers so that the texture of the processing can include more “clipper sound” when desired. Regardless of how you adjust the multiplex power controller, you can be sure that you will always meet the BS 412 requirements flawlessly.
The stereo encoder’s stereo sub-channel modulator can operate in normal double sideband mode (DSB) and in an experimental compatible single sideband mode (SSB) that is offered to enable users to compare and assess the two modes. Users who are required to comply with the ITU-R BS.412 multiplex power limits should note that SSB operation puts 3 dB more power into the stereo sub-channel than conventional DSB operation does. The 8600Si’s built-in ITU-R MPX Power Controller automatically compensates for this increase. The 8600Si includes a “ratings encoder loop-through” connection. This allows a ratings encoder with an AES3 digital input and output to be inserted between the output of the AGC before the analog-FM and HD processing paths split or between the output of the audio processing and the input to the stereo encoder. This keeps the audio level driving the ratings encoder as high as possible, minimizing the number of “low audio level” alarms that the ratings encoder generates.
A 10 MHz frequency reference input allows the stereo pilot tone frequency to be locked to GPS or another high-accuracy frequency standard. This improves the performance of single-frequency networks in areas where coverage of the transmitters overlaps. Analog Fallback to Digital control that allows Silence Sense to switch the active input from Analog to Digital if silence is detected in the analog input signal but not on the digital input signal. This function works vice versa as well on both analog and digital AES input. The silence sense parameters apply to both simultaneously and both detectors are available to drive the 8600Si’s tally outputs and sending SNMP Traps/Alerts.
The 8600Si includes a full-featured RBS/RBDS generator at no additional charge. The generator supports dynamic PS. It can be controlled via 8600S presets and an ASCII terminal server that can be connected to automation to support displaying title and artist.
Ethernet connectivity is standard, as is an easy to use PC remote control application that runs on Windows 2000, XP, Vista, 7, 8, 8.1 and 10 that can control many 8600Si’s on a TCP/IP network. 8600Si PC Remote software allows you to access all 8600Si features and allows you to archive and restore presets, automation lists, and system setups (containing I/O levels, digital word lengths, GPI functional assignments, etc.). In addition, programmable contact-closure (GPI) control plus ACSII terminal control via the 8600Si’s RS232 serial and Ethernet ports and give you total freedom to interface the 8600Si with your facility’s remote control infrastructure, whatever it might be.
Administrating and Monitoring
The SNMP (Simple Network Management Protocol) features allow you to monitor your Optimod’s status and to send Alarm notifications via your Optimod’s Ethernet connection to your network. The API interface allows you to use custom third-party applications (including automation systems) to recall presets, view status and set the controls.
Processing for Digital RADIO
Suitable for any digital transmission channel (such as DAB+, netcasts and HD Radio) that does not use pre-emphasis, the 8600Si Digital Radio processing chain offers an ITU-R BS.1770-3 Loudness Meter and Loudness Controller for use in countries that enforce a BS.1770 loudness limit on digital radio broadcasts. The 8600Si implements “true peak” control in the HD processing chain by oversampling the HD peak limiter’s sidechain at 256 kHz, which exceeds the recommendations in ITU-R BS.1770 for “true peak” metering. This allows the 8600Si to prevent clipping in a playback device’s analog signal path by predicting and controlling the analog peak level follow the playback device’s reconstruction filter to an accuracy of better than 0.5 dB. For typical program material, accuracy is 0.2 dB. Without true peak control, analog clipping can occur even if all peak values of the digital samples are below 0 dBFS. This phenomenon has also been termed “0 dBFS+.” Thanks to true peak control, sample rate conversion, unless it removes high frequency program energy or introduces group delay distortion, cannot cause sample peaks to increase more than 0.5 dB.
The HD Radio system generates a digital carrier that shares a given station’s allocated bandwidth with the analog FM carrier. The receiver crossfades between the analog and digital channels to minimize the effect of RF dropouts. This scheme requires audio processing for the two channels to be closely matched in texture to ensure that the receiver’s crossfades are seamless. Optimum peak limiting for the two channels is very different. The analog channel requires state-of-the-art pre-emphasis limiting to achieve competitive loudness and minimize pre-emphasis-induced high frequency loss. The digital channel, on the other hand, has no pre-emphasis but is heavily bit-reduced with the HDC perceptual codec. The highest available rate is 96 kbps and many broadcasters are now multicasting with two 48 kbps channels. This limited bitrate creates an entirely different set of requirements: the peak limiting must not use clipping because there is no bit budget available to encode clipping-induced distortion products. However, pre-emphasis limiting is unnecessary. The best technology for peak limiting the digital channel is look-ahead limiting, which can perform very clean peak reduction on flat channels, but which is unsuitable for pre-emphasized channels. OPTIMOD-FM 8600Si is an excellent solution to his dilemma because its AGC and stereo enhancement are shared between the two channels, while equalization, multiband compression/limiting and peak limiting are independent.
The analog FM path provides the improved MX peak limiter, overshoot compensation, stereo encoding, and composite limiting using Orban’s patented “Half-Cosine Interpolation” algorithm. The peak limiting is anti-aliased and uses sample-rates as high as 512 kHz. Meanwhile, the HD output receives low-IM look-ahead peak limiting, which we improved in the 8600Si to exploit some of the same new technology we designed for the FM analog processing chain. This look-ahead limiting is optimized to make the most of the limited bitrate codecs used digital radio and netcasting channels. By eschewing any clipping, the HD processing prevents the codec from wasting precious bits encoding clipping distortion products, allowing the codec to use its entire bit budget to encode the desired program material. For convenience, it is possible to couple the equalizer, HF enhancer and multiband compressor/limiter setup controls of the two paths, allowing them to be matched easily. This is useful in HD Radio installations where the station’s goal is to minimize the audibility of analog/digital crossfades at the receiver. However, the ability to adjust the analog FM and digital radio paths separately allows users more latitude to fine-tune their audio. For example, a broadcaster who believes that selling the advantages of HD Radio to the public requires an obvious, audible difference between the analog FM and digital channels can generate this “wow!” factor. Dual-path processing also allows the digital media processing to be independently tuned to minimize artifacts in low bitrate codecs, like those used in netcasting and HD Radio.
A built-in diversity delay of up to 16 seconds in the analog processing path simplifies installation in HD Radio facilities, freeing you from the need to use the delay line built into the HD Radio exciter. This allows you to use the 8600Si’ built-in stereo encoder and composite limiter to drive the analog FM transmitter, ensuring no-compromise analog- channel loudness. The diversity delay can be applied independently to any output emitting the analog-FM processing signal, so some outputs can be delayed while others are not. In addition to be adjustable via 8600Si PC Remote software, the diversity delay can also be adjusted remotely via the 8600Si’s control API or SNMP. This provides “hooks” that allow a compatible third-party HD monitor receiver to automatically achieve exact delay matching at the receiver by measuring the delay and correcting it as necessary.The 8600Si’s 64 kHz base sample rate allows it to provide up to 20 kHz audio bandwidth at its HD output. The HD bandwidth is user-settable between 15 and 20 kHz to optimize the processing for the codec employed in the digital chain. Many low bitrate codecs operate better when fed 15 kHz audio because this enables them to use their available bit bandwidth most efficiently. This is particularly true for low rates, like 32 kbps. However, at higher sample rates, full 20 kHz bandwidth provides the same bandwidth as typical source material, so the user may prefer to use it for these higher rates.
Although the 8600Si’ new peak limiter technology has narrowed the gap, the 8600Si’s digital output still sounds cleaner and more open than its FM output, particularly in the high frequencies — the analog channel is inevitably handicapped by the standard 50 and 75 microsecond pre-emphasis curves, which compromise its high frequency headroom. Using program material, we’ve measured as much a 9 dB difference in favor of the digital channel at high frequencies! Even after the processed passes through the codec, a significant amount of this audible superiority remains. Most HD Radio exciters require 44.1 kHz AES/EBU audio streams for both their analog-FM and digital inputs. The sample rates for both streams must be identical and must be locked to an external reference. This requires two AES/EBU outputs from a single-box processor. Because the output sample-rate on either or both of the 8600Si’ AES3 outputs can be locked to either the 8600Si’ sync reference input or to its AES3 input, the 8600Si fully meets the requirements. Moreover, because of the 8600Si’s built-in diversity delay on the analog-FM channel, it is possible (and usually desirable) to entirely bypass the analog-FM side of the HD Radio exciter and to use the 8600Si’ built-in stereo encoder and composite limiter to drive the analog FM exciter directly.