To bring out the best in the low bit-rate codecs used in netcasting, you should preprocess an Internet audio signal to condition it prior to encoding. The appropriate preprocessing has much in common with the preprocessing required for DAB, HD Radio™, CD mastering or digital satellite. OPTIMOD-PC can provide this processing.

Conventional AM, FM or TV audio processors that employ pre-emphasis/de-emphasis and/or clipping peak limiters do not work well with perceptual audio coders such as Orban OPTICODEC-PC® MPEG-4 AAC/HE-AACv2 streaming encoder. The pre-emphasis/de-emphasis limiting in these processors unnecessarily limits high frequency headroom. Further, their clipping limiters create high frequency energy — distortion — that the perceptual audio coders have to encode, wasting bits. None of these devices has the full set of audio and control features found in OPTIMOD-PC.

Peak clipping sounds bad even in uncompressed digital channels because these channels do not rely on pre-emphasis/de-emphasis to reduce audible distortion. Instead of peak clipping, OPTIMOD-PC uses look-ahead limiting to protect the following channel from peak overload.

OPTIMOD-PC’s PreCode™ technology manipulates several aspects of the audio to minimize artifacts caused by low bitrate codecs, ensuring consistent loudness and texture from one source to the next. PreCode includes special audio band detection algorithms that are energy and spectrum aware. This can improve codec performance on some codecs by reducing audio processing induced codec artifacts, even with program material that has been preprocessed by other processing than OPTIMOD. There are several factory presets tuned specifically for low performance, low bitrate codecs.

Unlike some other codec preprocessors, PreCode™ does not suck the punch and life out of music. Instead, PreCode™ strikes an artistic balance between liveliness and artifact reduction, ensuring that the cure is never worse than the disease.

OPTIMOD-PC is also an excellent mastering processor, offering soft knee multiband compression with knee and ratio controls available separately for each band. OPTIMOD-PC’s low-IM look-ahead limiter can typically achieve 12 dB of gain reduction before it produces objectionable artifacts — this limiter is exceptionally loud and clean.

Digital mixing is crucially important to a netcaster who needs to control commercial content and insertion. Unlike most sound cards, OPTIMOD-PC allows you to mix an analog source, two digital sources and two Wave sources. For example, you could run a playout system on your computer while using the three hardware inputs for a live microphone feed, commercial insert, and network insert. Or you could run the commercial insert playout software on the same computer as the main playout system, using OPTIMOD-PC’s second Wave input to separately route the outputs of the two playout systems to the card. In most cases, an external mixer isn’t needed, making OPTIMOD-PC a more economical system solution than a low-priced sound card combined with external hardware. OPTIMOD-PC is also perfect for podcast production.

For applications like commercial insertion, an API provides complete remote administration over TCP/IP and/or Serial. The OPTIMOD-PC Service application hosts a TCP/IP terminal server and a serial interface to allow external control of the OPTIMOD-PC cards from either a software Telnet/SSH terminal client, a custom third party application, or a hardware device such as a Broadcast Tools SRC-16. All OPTIMOD-PC Mixer and System Controls are accessible and all commands are simple text strings. You can adjust and monitor levels, tweak the processor’s sound, save and recall presets, and more. Password security is provided.

OPTIMOD-PC comes with over 20 great-sounding presets that make it easy to create a sonic texture that’s just right for your target audience. If you want to customize a preset, you can start with an easy LESS-MORE control. If that’s not enough, tweak over 50 parameters to hone your sound to perfection. OPTIMOD-PC’s deep interface will never hold you back as your processing expertise increases, yet its carefully crafted design insulates you from the details if you need great sound right now.

You can expect a considerable increase in loudness from OPTIMOD-PC processing by comparison to unprocessed audio (except for audio from recently mastered CDs, which are often overprocessed in mastering). Broadcasters generally believe that loudness relative to other stations attracts an audience that perceives the station as being more powerful than its competition. We believe that the same subliminal psychology holds in netcasting.

Figure 1-1 shows a 15-minute snapshot of program audio as it emerged from the on-air mixer of a major Los Angeles radio station. Source material included music, speech, and commercials. Notice the large inconsistency in peak and average level between one program source and the next. Figure 1-2 shows the same material after being processed through OPTIMOD-PC, using the Gregg preset. Notice that program levels are now consistent from source to source.

It is important to understand that peak or average file normalization does not accomplish what OPTIMOD-PC processing can. Normalization applies a fixed loudness adjustment to the entire fileit’s like setting a volume control once and only once. On the other hand, OPTIMOD-PC processing constantly adjusts spectral balance and loudness to achieve a consistency that brands your sound. This particularly important during transitions from one program element to the next and is one of the key techniques that major-market radio stations use to achieve their polished, “produced” audio texture.