Introducing Optimod-FM 8500: Orban's new flagship processor and the next step beyond the Optimod-FM 8400. The 8500 builds on the proven, competitive sound of 8400 version 3 while adding features that make it the ideal choice for FM stations simultaneously transmitting iBiquity's HD Radio®, Eureka 147, or a netcast (where it works particularly well with Orban's Opticodec-PC® LE). "Under the hood," we redesigned all of the circuitry using the latest components. We also doubled the DSP power, so the DSP not only supports the new features but also provides comfortable headroom for future DSP improvements.
Featuring versatile five-band and two-band processing for both analog FM transmission and digital radio, the 8500 provides the industry's most consistent sound, track-to-track and source-to-source. This consistency allows you to create a sonic signature for your station with the assurance that your signature will stay locked in, uniquely branding your sound.
The 8500 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 8400 version 3 factory presets, plus some new ones designed by Bob Orban and Greg Ogonowski to please any broadcaster. Although the factory presets are fully competent "out of the box," you can customize them with easy one-knob LESS-MORE control or with more than 60 advanced controls, whose versatility will satisfy even the most finicky on-air sound designer. If you have created custom presets for your 8400, you'll find that they import perfectly into the 8500, retaining your carefully crafted sound.
If you choose to use the 8500's superb DSP-based stereo encoder and composite limiter, be assured that they deliver an FM analog signal that is always immaculately clean and perfectly peak limited, with full spectral protection of subcarriers and RDS/RBDS regardless of the amount of composite limiting.
Processing for digital radio/netcast (DR) is now supplied standard. We increased the base sample rate of all processing to 64 kHz so the DR output can readily provide 20 kHz audio bandwidth for those who prefer it. Moreover, a built-in diversity delay in the analog processing path vastly improves installation versatility in HD Radio plants, freeing you from the need to use the delay line built into the HD Radio exciter. This allows you to use the 8500's built-in stereo encoder and composite limiter to drive the analog FM transmitter, ensuring no-compromise analog-channel loudness.
The 8500's digital radio processing contains look ahead peak limiting that operates in parallel with the FM-channel peak limiting. We optimized the look-ahead limiting to make the most of the limited bit-rate codec typically used in the digital channel. By eschewing any clipping, the digital radio 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.
The look-ahead limiter receives the output of a new mixer that sets the balance of each processing band for the digital channel, independent of the balance in the FM processing. 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.
We haven't forgotten pure analog FM broadcasters. If you defeat the diversity delay, you'll find that the 8500's base throughput delay has decreased by almost 4 milliseconds compared to the 8400. This makes off-air headphone monitoring even more comfortable for talent. Of course, we've retained the 8400's "headphone monitor" output option, which now has a negligible 2-millisecond delay regardless of the processing structure on-air. We've also added the "ultra-low-latency" structure first introduced in Optimod-FM 8300. This structure yields about 3 milliseconds of throughput delay at the expense of lower loudness.
Ethernet connectivity is now standard, as is a new, easy to use PC remote control application that runs on Windows 2000 and XP and that can control many 8500s on a TCP/IP network. In addition, RS232 serial control and programmable contact-closure (GPI) control give you total freedom to interface the 8500 with your facility's remote control in-frastructure, whatever it might be.
User interface improvements round out the package. We started with the 8400's easy to use joystick, knob, and button navigation system and added a bright, active-matrix color LCD that makes it easier to program the 8500 from its front panel. The panel's eye-catching new metallic blue styling makes the processor look as great in your rack as it sounds on the air.
For our European customers, a second generation ITU BS 412 multiplex power controller greatly improves the accuracy of the process as measured on industry standard monitoring instruments, yielding the best possible coverage while flawlessly complying with the standard.
PROCESSING FOR HD RADIO
The HD Radio system generates a digital carrier that shares a given station's allocated bandwidth with the normal 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 preemphasis limiting to achieve competitive loudness and minimize preemphasis-induced high frequency loss. This usually implies use of sophisticated distortion-canceled clipping. The digital channel, on the other hand, has no preemphasis but is heavily bit-reduced with the HDC perceptual codec. The highest available rate is 96 kbpsand many broadcasters are now multicasting with two 48 kbps channels.
This limited bit rate 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, preemphasis limiting is unnecessary. The best technology for peak limiting the digital channel is therefore look-ahead limiting, which can perform very clean peak reduction on flat channels, but which is unsuitable for pre-emphasized channels unless it is used as one element in a sophisticated system that also includes distortion-canceled clipping (as in the 8500s analog FM limiter).
Orban's solution to this dilemma is Optimod-FM 8500: a single box processor where AGC, stereo enhancement, equalization, and multiband compression/limiting are shared between the two channels. Because these elements are mainly responsible for the station's signature sound texture, this ensures that the analog and digital channels will crossfade unobtrusively regardless of the processor's settings—great news for stations that daypart their processing.
After this processing, the signal splits off into two paths for peak limiting. The analog FM path provides distortion-canceled clipping with intelligent distortion control, overshoot compensation, stereo encoding, and composite limiting using Orban's patented "Half-Cosine Interpolation" algorithm. Meanwhile, the HD output receives low-IM look-ahead peak limiting that operates in parallel with the analog FM peak limiting. This look-ahead limiting is optimized to make the most of the limited bit-rate 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.
The digital processing chain also allows the station to insert a high frequency shelving equalizer either before or after the look-ahead limiter. Inserted before, it can reduce codec artifacts caused by excessive brightness in the previous processing. (This brightness is frequently introduced to compensate for HF limiter-induced roll offs in the analog chain.) Inserted after, it can realize the same advantage and reduce codec-induced overshoot too. A separate "digital path" mixer for the various bands of the multiband processing provides an alternate means for determining audio texture and controlling codec artifacts. Fortunately, the Spectral Band Replication® technology used in the HDC codec is far more forgiving of bright-sounding program material than was the technology used in the first-generation iBiquity codec (PAC). This allows the user to adjust the digital channel's audio texture far more freely in the quest for the "perfect sound."
The 8500'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 bit rate 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.
Auditioned directly, the 8500's digital output sounds dramatically cleaner and more open than its FM output, particularly in the high frequencies—it's obvious just how much the analog channel is handicapped by the standard 75 microsecond preemphasis curve, which compromises its high frequency headroom. Using program material, we've measured as much a 12 dB difference in favor of the digital channel at high frequencies! Even after the digital signal passes through the 96 kbps codec, a significant amount of this audible superiority remains—the HD Radio system really does provide noticeably better sound to the consumer.
The first-generation iBiquity exciter requires 44.1 kHz AES/EBU audio streams for both its analog-FM and digital inputs. The sample rates for both streams must be identical. This requires two AES/EBU outputs from a single-box processor, both of which can be locked to an external AES reference signal. Because the output sample rate on either or both of the 8500's AES3 outputs can be locked to either the 8500's sync reference input or to its AES3 input, the 8500 fully meets the requirements. Moreover, because of the 8500'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 iBiquity exciter and to use the 8500's built-in stereo encoder and composite limiter to drive the analog FM exciter directly.
0 komentar:
Posting Komentar