frequency dependent limiter
Split band Limiter
multiband clipper
frequency clipping
The Aphex Systems Model 720 / 722 Dominator II is a stereo MultiBand peak limiter designed to fit a wide range of applications. Through the use of MultiBand techniques along with new proprietary circuits, the audibility of limiting action has been greatly reduced, especially when compared to conventional limiters. This means that greater limiting depth is possible, resulting in higher loudness with maintained audio quality. At virtually any limiting depth, the Dominator II is free of "hole punching", "dullness", and most other effects normally associated with limiters. As a peak overshoot protection limiter, the Dominator II is undetectable in line while it absolutely prevents peak levels from exceeding a user settable output level. In addition, the desired limiting effects of greater audio density and increased "punch are readily available with the Dominator II.The Model 722, for broadcast use, has the Pre and De-emphasis circuitry, while the Model 720 Does not.
Multiband vs Wideband Processing 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 be 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 flexibility to shape the sound while quickly and easily achieving the goal of consistent, effective limiting
ALT (Automatic Limit Threshold) A MultiBand processor splits the audio into separate bands, limits each band individually and then sums the bands together again. Even though each band's peak output is predictable, summing the bands together produces an unpredictable peak output.
One conventional approach to making the summed output predictable is to use a wideband limiter after the summing. This, however, introduces all the drawbacks of wideband limiting discussed above.
Another approach is to use a clipper on the summed output. This causes too much clipping distortion if the summed output is too high. In order to avoid this distortion the limiters' thresholds are set very far below the clipper threshold. The drawback is a loss of loudness and, due to the lower thresholds, much greater amount of processing.
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 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.
It should be noted that there is only one ALT circuit controlling both channels equally. This provides global stereo balance and imaging by assuring that both channels always limit at the same threshold. This does cause an interaction if the Dominator II is used as two independent channels. Therefore, we do not recommend such a practice
Model 722 Pre- and De-emphasis Pre-emphasis is an equalization curve expressed as a time value based on the ratio of a resistor and capacitor. The higher the value, the greater the equalization. It has been employed as a noise reduction technique for broadcast and transmission links. There are primarily two world standards- 50 and 75 microseconds.
The Dominator II Model 722 has separately switchable pre and de-emphasis curves. When pre-emphasis is switched in, either 50 or 75 microseconds, the equalization curve is added after the input stage and before the limiters. When de-emphasis is switched in, the complementary de-emphasis curve is inserted after the final clipper and before the output stage.
When both pre and de-emphasis are switched in, the frequency response of the output is flat. When the input is below threshold and as the input increases above threshold the output takes the shape of the de-emphasis curve.
When both pre and de-emphasis are switched out, the Model 722 works exactly like the Model 720.
Multiband limiter with automatic limiting threshold (ALT) compensation
A multiband audio frequency signal limiting apparatus suitable for use in a wide range of applications is disclosed. An input signal is divided into discrete frequency bands (any practical number is suitable) which are each passed through a separate limited and subsequently summed to obtain an output signal. The summed output signal is fed into an automatic limit threshold circuit which generates a third signal, the Automatic Limit Threshold (ALT) signal, which modifies a common limiting threshold reference for the bands. This causes the bands to limit at a higher or lower threshold level and the band output levels to increase or decrease in direct proportion to the threshold level of limiting. The ALT signal cause the bands to limit at a lower threshold when the energy content of the various bands would combine toward higher values, which could thus generate a larger than desired output signal level. In this way, the summed output signal will be servoed towards one hundred percent level regardless of the input audio frequency bandwidth (and consequently the individual relative band energy content).
Behringer DSP9024 multiband limiter compressor process
Behringer DSP9024 multiband limiter compressor process
multi-band processing
Behringer EX2200 Dualfex Pro is a sound enhancer
Behringer Ultramizer Pro DSP1424P Multiband compressor/limiter
Behringer DSP1424P Ultramizer Pro
Behringer DSP1424P Ultramizer Pro
Behringer DSP1424P Ultramizer Pro
The Ultramizer Pro DSP1424P confers the added value of 24-bit resolution to the already hugely popular Ultramizer Pro
DSP1400P, plus much more. Its powerful new DSP engine lets you add multi-band, program-adaptive compression and limiting for both low and high frequencies while at the same time remaining absolutely 'inaudible'. No matter if you want to increase the loudness of your mastering recording or double the loudness of your PA system without adding more amplifier power, the DSP1424P is the perfect tool. A peak limiter protects against any clipping and dangerous sound pressure levels and the built-in 3D stereo surround processor provides unbelievable spatial enhancement and improved stereo imaging, giving your mixes that often sought-after extra 'gloss', while the noise reduction system keeps things clean. Despite the sheer scope of added functions and improved functionality, the DSP1424P is still super easy to use and operate, letting nothing come between you and your music.
Features
Ultra high-performance digital multiband loudness maximizer / sound program enhancer powered by a 24-bit DSP
Doubles the loudness of your recordings and sound reinforcement systems without any distortion
Ultimate mastering machine maximizes signal energy with absolutely 'inaudible' and transparent compression
Variable band-split compression eliminates virtually any gain intermodulation effects, such as 'bass pumping' etc.
'Intelligent' digital limiter protects against any clipping and dangerous sound pressure levels
Built-in denoiser and exciter for noise-free and ultra transparent sound
3D stereo surround processor provides unbelievable spatial enhancement and improved stereo imaging
Super bass enhancer psycho-acoustically creates an incredible bass sound below your loudspeaker’s frequency range
Incorporated leveler for constant average output level while retaining the instantaneous dynamics
Free Ultramizer software downloadable from Behringer
24-bit A/D and D/A converters with 64/128 times oversampling for ultra-high headroom and resolution
Internal 24-bit processing with professional 46 kHz sampling rate
Servo-balanced inputs and outputs on gold-plated XLR and TRS connectors for high signal integrity
50 programmable user presets for instant recall
Accurate eight-segment LED level and gain reduction meters for optimum performance
'Future-proof' software-upgradeable architecture
Full MIDI capability allows real-time parameter control and program selection
High-quality components and exceptionally rugged construction ensures long life and durability
Designed in Germany. Manufactured under ISO9000 certified management system
