The OPTIMOD-FM 8500 Digital Audio Processor Orban’s all-digital 8500 OPTIMOD-FM Audio Processor can help you achieve the highest audio quality in FM stereo broadcasting. Because all processing is performed by high-speed mathematical calculations within Motorola DSP56367 24-bit digital signal processing chips, the processing has cleanliness, quality, and stability over time and temperature that is unmatched by analog processors. OPTIMOD-FM 8500 is descended from the industry-standard OPTIMOD-FM audio processors. Thousands of these processors are on the air all over the world. They have proven that the “OPTIMOD sound” attracts and keeps an audience even in the most competitive commercial environment. Because OPTIMOD-FM incorporates several audio processing innovations exclusive to Orban products, you should not assume that it can be operated in the same way as less sophisticated processors. If you do, you may get disappointing results. Take a little time now to familiarize yourself with OPTIMOD-FM. A small investment of your time now will yield large dividends in audio quality. The rest of Section 1 explains how OPTIMOD-FM fits into the FM broadcast facility. Section 2 explains how to install it. Section 3 tells how to operate OPTIMOD-FM. Section 4 through Section 6 provides reference information. OPTIMOD-FM was designed to deliver a high quality sound while simultaneously increasing the average modulation of the channel substantially beyond that achievable by “recording studio”-style compressors and limiters. Because such processing can exaggerate flaws in the source material, it is very important that the source audio be as clean as possible. For best results, feed OPTIMOD-FM unprocessed audio. No other audio processing is necessary or desirable. If you wish to place level protection prior to your studio / transmitter link (STL), use the Orban Optimod 6300 or Optimod-PC 1101. These processors can be adjusted so that they substitute for the AGC circuitry in OPTIMOD-FM, which is then defeated. OPTIMOD-FM 8500 is available in two front-panel configurations—the 8500 has a full-featured front panel, while the 8500X has a blank front panel and must be con- trolled by Orban’s PC Remote application running on Microsoft Windows XP, 2000 (SP3), or later. Both units have identical sound and features except for the difference in their front panels. Both units run the same software. If you are setting up an “X” version, refer to Administering the 8500 through its Serial Ports or Ethernet (starting on page 2-43) for instructions on how to use the 8500X’s serial port #2 to set up communications between your computer and the 8500X. Both the 8500 and 8500X simultaneously process for analog FM and digital channels like the iBiquityTM HD RadioTM system, Eureka 147 (DAB), DRM, or netcasts. The 8500’s HD output provides look-ahead peak limiting that is optimized to make the most of limited bit-rate codecs used in many digital radio systems. By eschewing any clipping, the HD output 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. Thanks to a base sample rate of 64 kHz throughout the 8500’s processing, the HD output can be set for audio bandwidths between 15 and 20 kHz. Many codecs operate better when fed 15 kHz audio because this enables them to use their available bit bandwidth most efficiently by concentrating on the part of the audio spectrum that is critical to perceived audio quality. 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 you may prefer to use it for rates of 96 kbps and above.