The panel of the 290RX divides the unit's functions up into two categories: Signal Restoration and Noise Reduction. The Harmonic Restoration Processor and the Spectral Restoration Processor are part of the Signal Restoration section. The dynamic filter and downward expander make up the Noise Reduction section. Bypass switches on the 290RX allow you to bypass the Signal Restoration section and/or the Noise Reduction section. They are positioned such that A/B comparisons are easy to do.
A "Detail" position on Signal Restoration bypass switch lets you hear only what is coming out of the Signal Restoration circuitry. If you flip the switch to "Detail" and turn the Spectral Level to zero, all you'll hear is the output of the Harmonic Restoration circuitry. Like-wise, if you turn the Harmonic Level to zero and leave the Spectral Level up, all you'll hear is what the Spectral Restoration Processor is doing. This helps let you know exactly what it is you're adding to the input signal.
Along with a Harmonic Restoration Level control there is a "Tuning" control. This control sets the frequencies that will be sent to the harmonic generator. Its range is from 1kHz to 5kHz. If set to 2kHz, all frequencies above 2kHz are sent to the generator. The "Level" control determines how much of the Harmonic Restoration is mixed with the main signal.
Cranking up the Harmonic Restoration Level has a much more subtle effect that doing the same with the Spectral Restoration Level. For most of the production-type of audio we sent through the box (voice, music, voice mixed with music), Spectral Restoration seemed to do the job just fine without the help of Harmonic Restoration. The manual does suggest heavy Harmonic Restoration as "particularly useful to make percussion instruments 'cut' through a mix while minimally increasing their peak levels, and to enhance the realism and apparent bandwidth of sampled instruments playing single lines (like individual brass, woodwind, and stringed instruments)." Harmonic Restoration does give an "edge" to whatever you apply it to, but it remains a more subtle effect compared to the Spectral Restoration.
Finally, after you've "spectrally" and "harmonically" restored your signal, the 290RX's Dynamic Single-Ended Noise Reduction circuitry adds a nice finish. Noise reduction is achieved by using a downward expander with the program-controlled (dynamic) low-pass filter. While processing some scratchy old records, we found the noise reduction circuitry to be extremely effective. When Spectral Restoration was added without noise reduction, the noise became more apparent. When the noise reduction was kicked in, not only was added noise eliminated, but the original noise seemed to be reduced as well and overall quality of the source greatly improved.
Threshold and ratio controls for the expander are provided for each channel. You also get a threshold control for the dynamic, low-pass filter. An LED Dynamic Filter Display indicates the bandwidth of the filter which helps in setting the filter threshold. The range of the filter is from 1.4kHz to beyond 40kHz. The other meter on the unit indicates the amount of gain reduction produced by the expander. Each channel has its own LED meter for the filter and the expander. The unit has a Stereo Couple/Independent switch, but it only affects the gains of the expanders.
All things considered, the 290RX is a nice addition to any production room. Dubbing all agency spots through the unit easily and quickly enhances any "muddy" spots while doing some noise reduction at the same time. The same benefits are achieved when using the 290RX to process oldies being dubbed to cart. Using Harmonic Restoration on telephone audio is beneficial because the added harmonics tend to give the audio a wider bandwidth which is helpful with muddy phone tracks. Utilizing the noise reduction on the processed signal helps clean it up.
We sent a mike through the 290RX with restoration and noise reduction active and were able to come up with some nice settings that offered a crisp sound while dramatically reducing background noise. The 290RX would work well as a control room mike processor where a crisp and quiet sound is desired.
The unit itself is very quiet with specs indicating noise at the output less that -110dB below clipping with the Spectral Level and Harmonic Level set to less than five and the noise reduction active. Frequency response is 20Hz to 20kHz, and total harmonic distortion is less than .1%. The 290RX takes up two rack spaces and lists for $1,200. And guess what? The panel is black and gray instead of that familiar Orban blue.