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The 9721 is an Aphex Dominator™ II Multiband Peak Limiter module which installs in one space of the Aphex Model 9000 rack or compatible dbx 900 series rack.

The Dominator II is a single channel Multiband Peak Limiter with zero overshoot which acts like a "brick wall". Once the PEAK CEILING is set, there is no higher amplitude in the output. Awareness of headroom limitations and the price of exceeding those limitations is important for any audio application and critical for most (especially digital). The Dominator II allows the user to work confidently, creatively, and quickly by freeing the user from the fear of peak overload.

In addition to providing peak protection, the Dominator II may be used to gain greater loudness. Compared to conventional limiters, the Dominator Ii will provide at least 3 to 6 dB greater loudness with higher sound quality.

Providing this "brick wall" and loudness, while retaining complete fidelity, is the art and science of the Dominator II.

A very significant problem with wideband processing is "spectral gain intermodulation" which occurs when one part of the spectrum controls the level of another part. A typical situation is a vocalist being "sucked down" every time the kick drum hits. Since most energy is contained in the lower frequencies, they tend to control the level of the entire spectrum. When the lower frequencies are above the limit threshold the higher frequencies are attenuated thus causing the output to sound dull.

Multiband processing solves these problems by splitting the audio into two or more frequency bands and processing each band separately. However, more bands often result in many more parameters to control including a method of summing the bands together again. While giving the user flexibility, it also requires different settings for almost every different source.

The Dominator II uses program dependent, intelligent circuits to reduce the number of controls. The user, therefore, has has flexibility to shape the sound while quickly and easily achieving the goal of consistent, effective limiting.

The Dominator II uses a patented method to produce a predictable peak output while maintaining maximum loudness without audible distortion — the Automatic Limit Threshold (ALT). The outputs of the three bands are summed and sent to the ALT detector circuit. If the sum exceeds a reference value, the ALT reduces the thresholds of the individual limiters. When the summed output falls below the reference value the limit thresholds return to their original setting.

The ALT circuit has a self-adjusting finite attack time. The amount of time it takes to lower the thresholds of the limiters is the length of time the limiters' overshoot may be in the clipper. The reference value of the ALT in relation to the clipper determines the depth of clipping.

Both parameters are set by the DENSITY control. When the DENSITY control is set higher, the ALT reference gets closer to clipping, and the attack time is slower, producing more clipping. The opposite occurs when the DENSITY is set lower. The "0 RCH" position for the DENSITY control emulates the standard parameters of the original Studio Dominator Model 700, and is recommended for general use.