8400 OPTIMOD-FM Digital Audio Processor Orban’s all-digital 8400 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 DSP56362 Digital Signal Processing chips, the processing has cleanliness, quality, and stability over time and temperature that is unmatched by analog processors. OPTIMOD-FM 8400 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 8200ST OPTIMOD-Studio Compressor/Limiter/HF Limiter/Clipper. The 8200ST can be adjusted so that it substitutes for the broadband AGC circuitry in OPTIMOD-FM, which is then defeated. OPTIMOD-FM 8400 is available in two main configurations—the 8400 has a full-featured front panel, while the 8400/PD has a blank front panel and must be controlled by Orban’s PC Remote application running on Microsoft Windows 98 or later. Both units have identical sound and features except for the difference in their front panels. Both units run the same software. Both the 8400 and 8400/PD can accept Orban’s HD (“High-Definition Digital Radio”) hardware plug-in, 8400HD. 8400HD adds an extra AES/EBU output to drive the digital channel in the iBiquity system. This output provides look-ahead peak limiting that oper-ates in parallel with the FM peak limiting. The look-ahead limiting is optimized to make the most of the limited bit-rate codec used in the iBiquity system’s digital channel. By eschewing any clipping, the HD output prevents the codec from wasting precious bits encoding clipping distortion products, allowing the codec to instead use its entire bit budget to encode the desired program material. 15 kHz band-limiting on the digital output also optimizes the operation of the low bit-rate codec. By not wasting bits encoding the 15-20 kHz frequency range that few radio listeners can hear, the codec instead provides higher quality encoding of the crucial 20-15,000 Hz band. 8400HD also adds a second analog output to the 8400 system. This can be configured to emit the 8400’s low-latency monitor signal, or to emit the signal that is processed for the HD digital channel.