by Jerry Vigil
It comes from Orban and it's called the "290RX Adaptive Enhancement Processor." In a nutshell, the 290RX is a stereo processor consisting of an equalizer, of sorts, which is called the Spectral Restoration Processor. You also get a harmonic generator which is referred to as the Harmonic Restoration Processor. This is rounded off with a single-ended noise reduction circuit. You get separate controls for left and right channels and the ability to use all three functions simultaneously, any one of them by itself, or any combination of the three. The manual describes the 290RX as a processor that "brings sound to life by increasing the definition, detail, and intelligibility of both single tracks and mixed program material."
When audio is pumped into the 290RX, it hits a program-controlled high pass filter or dynamic filter. If there is a lot of high frequency energy in the input, the filter's bandwidth opens up to let all the highs through. When there is little high frequency energy (as with a muddy sounding, eleventh generation dub), the bandwidth of the filter decreases and filters out high frequency hiss. This filter comes with a threshold control and LED meter for each channel. From this filter the signal is sent simultaneously to both the Spectral Restoration Processor and the Harmonic Restoration Processor which function independently of each other. From these processors, the signal then hits a downward expander which, together with the dynamic filter, comprises the noise reduction section of the 290RX.
The equalizer section, or Spectral Restoration Processor, of the 290RX is perhaps the most useful part of the unit. You may recall an earlier review of the Tailor Dynamic Equalizer (May '90) in which we looked at a device that analyzes incoming audio and automatically "equalizes" it based upon the spectral makeup of the input. The EQ section, or Dynamically-controlled Spectral Restoration section, of the 290RX is similar. The major differences are that the 290RX only deals with the upper frequencies, and those frequencies are pre-selected by the 290RX thus eliminating all user controls except for one, the Spectral Restoration Level. Increasing this level acts much like boosting highs with an equalizer. The trick the 290RX does here is an analysis of the incoming signal which dictates to the processor the amount of high frequency boost that should occur. More specifically, a high-pass filter picks out the highs that are present in the main signal. The output of this filter is then added to the main signal. How much of the filter's output is added is determined by how much high frequency energy is present to begin with. The more highs that are present in the input, the less effect this function has. Likewise, if an input is lacking highs, the processor reacts by increasing the mix of this high-pass filter with the main input to "bring the audio to life."
This program controlled equalizer is very handy for processing oldies as they're being dubbed to cart. Since the desired amount of high end boost will vary from record to record, depending upon how much highs there are to begin with, the result is more consistent EQ on dubs of songs of varying quality. We also passed several agency spots through the 290RX to see if the same effect occurred, and it did. As you know, many dubs received from agencies are high speed dubs, several generation dubs, or just poor dubs which lack nice, crisp highs. Spectral Restoration can add just the right amount of high end boost without having to deal with several EQ controls. There's just one knob to twist, and once it is set, you can do dub after dub and let the 290RX adjust the amount of high end boost automatically.
The other form of high frequency processing the 290RX performs is called Distortion-cancelling Harmonic Restoration. If you're unfamiliar with how harmonic "exciters" work, you might find the technical aspects somewhat intriguing. While this area of sound is moderately complex and quite interesting, we'll spare the lofty details and offer the basics. When you hit middle C on a piano, the vibrations from that strike tend to make other strings in the piano vibrate, specifically those strings representing frequencies that are multiples of the frequency of middle C. One octave up from that middle C happens to be middle C's "second harmonic," and those strings vibrate at precisely twice the rate (or frequency) of the strings at middle C. If you strike middle C while deadening the strings of that second C, you eliminate the "second harmonic energy" of middle C on a piano. Taking this out of the world of music, if you have a 1,000 cycle tone, its second harmonic is at 2,000Hz, it's third harmonic is at 3,000Hz, and so on. In the most basic terms, a harmonic exciter analyzes the frequencies at the input and generates second harmonics of those frequencies, then adds them to the original signal. In effect, the exciter is literally creating higher frequencies that don't exist in the original signal. This is a fancy way to boost highs, but the result isn't the clean, pitch-shifted output you might expect. This is because of several other aspects of harmonic generators that are beyond the scope of this review. However, we will touch on it to the following extent:
Orban is very proud of one particular aspect of their Harmonic Restoration circuitry. Their patented circuitry eliminates difference-frequency intermodulation. While this technical gaga probably won't affect your life in the near future, we'll note that harmonic generators tend to not only produce second harmonics, but also two types of distortion which are known as sum-frequency intermodulation and difference-frequency intermodulation. Orban's special concoction gets rid of the difference-frequency IM (which is supposedly less desirable than the other type) and leaves only the second harmonics and sum-frequency intermodulation. Call it what you want, but the output of the Harmonic Restoration circuitry is nothing more than pure distortion, but it just happens to be of such a nifty type that when it is mixed with the original signal, there is a definite "brightening" of the signal that you can't achieve with EQ.
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