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Field Report: Orban Optimod-FM 8600
This processor is excellent and can be counted on to represent the source. Processing structure is very similar to the 8500, so it was easy to adapt to the 8600. Any changes are in the DSP - the 8600 uses a DSP board with about three times the processing power of the 8500's board. As chip designs and algorithms improve, we will always experience new and better sound, and that is evident in the first listening. The most notable change is in the peak limiter.
The MX Technology Peak Limiter aims to achieve clean, crisp audio using a multi-stage approach. The first stage mentioned in the manual is a pre-limiter to control low and high frequency peaks prior to the main peak limiter, which is the next stage. The main peak limiter uses a psychoacoustic masking model to help prevent clipping distortion from becoming audible.
All new presets with MX in their names use the new limiter. The non-MX presets are the same as those found in the 8500 and were primarily included because they have much lower delay than the MX presets. This may be required if live talent is relying on an off-air feed to drive headphones during remote broadcasts. The non-MX presets also provide a nice base for comparison purposes. Another way to determine which presets use the MX limiter is to navigate to the distortion tab, where a different set of controls appear.
I performed a number of listening tests using the Gregg and the Gregg_MX presets along with my own custom preset pair. There is a noticeable audible difference between the presets. The energy in the high end is subtle, but the clarity is improved. This effect is more pronounced if more aggressive settings are used, though the tradeoff between distortion and clarity also increases. My first test was to push the multiband clipping harder in the MX. I usually run this conservatively at 0dB to 1dB. When using an MX preset, I was surprised that I was able to push 3dB and maintain acceptable sound quality; while in the non-MX presets, the word grunge comes to mind. Be aware than other settings (mostly individual band compressor thresholds) change between MX and non-MX factory presets because Orban's programmers tried to keep the mid-frequency and low-frequency balances consistent between similarly named MX and non-MX presets while still exploiting the MX limiter's ability to achieve 2 to 3dB more high frequency energy than the 8500-style limiter. I learned this with a custom setting to push the bass. Without making any other difference to the compressors, I changed the equalizer settings, boosting the bass to the maximum of 12dB in the LF Shelf and 10dB in the low band centered around 266Hz. Changing the pre-limiting and bass-limiting settings, I was able to hear the gain reduction of the low end and how the distortion products changed. Surprisingly the distortion was not as unacceptable as one would expect. The high end maintained clarity much better than the predecessors. As for the non-MX presets, do not try this at home.
There is one operation that I was unable to perform and test. Orban provides a compatible single sideband operation for their composite feed. Others have written on this subject and I am unable to test it with our setup. It is a compelling excuse to move our equipment to the transmitter site, but space limitations at the sites and IBOC operation preclude our doing that.
I cannot go through an evaluation without commenting on the documentation. In the case of Orban, it is a nice addition. All documentation is provided in PDF format. Both a godsend and a curse, PDF is nice in that it is searchable. The bookmarks all link to appropriate sections. The extra work necessary is to link the index, especially with the section-page number format that is used. The best part of the documentation is the detail. It is worth the time to browse, read, and absorb the content, especially the section titled Introduction to Processing.
The move toward higher quality audio on FM is nice to see. The new Orban 8600 is on the right path to providing this quality. We will continue to see and hear improvements as technology improves. I look forward to what manufacturers will do next.
Eisenhamer is chief engineer of Lincoln Financial Media Co. of California.
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