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ML8000 Next Generation Limiter Technology

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The ML8000 Advanced Limiter is the next generation of limiter technology, using two completely separate stages of processing for significantly improved peak level adjustment. The ML8000 has plenty of tricks up its sleeve, as discussed in this edition of Colin’s Corner.

Overview

The first stage of the ML8000, the Multi-band Limiter, uses 8 bands of active processing for superior phase response over traditional cross-over based processing. Each band has its own gain and threshold (output ceiling) control. Additional overall band controls include release time and limiter modes, calibrated similarly to the original highly acclaimed McDSP ML4000 limiter (just in an 8-band fashion !!). An additional focus mode provides subtle articulation changes in how each band tracks and limits the incoming signal.

The second stage of the ML8000, the Master Limiter, is a precise recreation of the patented ML4000 limiter algorithm, right down to the limiter modes. The Master Limiter also includes filter design enhancements to further reduce peak distortion.

Active vs. Crossover-based Processing

SA2 ModeBecause the ML8000 offers so many bands of processing, its design has to do a good job of preserving phase without increasing overall latency. For these reasons, the ML8000 uses an active network to process all 8 bands, instead of the traditional cross-over based approach. The result is mighty compelling. Not only does the ML8000 offer less phase distortion (none if not ‘active’), it does so with a minimal penalty to latency. In fact the ML8000 is still one of the best in its class when it comes to latency – barely over 1 msec of delay from input to output.

Even though processing is active-based, the user interface is still setup as a more conventional cross-over based process. There are 7 ‘cross-over’ frequencies that determine the range of each band’s processing. Note each band’s minimum width is approximately one octave, so when an adjacent band is adjusted, it may cause other cross-over frequencies to update if their proximity to each other is less than this 1 octave minimum.

Pre-Filtering

Although the multi-band processing is completely active, there are two static pre-filters (high pass and low pass) that can be enabled by pressing the HPF and LPF icon buttons at the extreme left and right hand side of the frequency response plot. The high pass filter (HPF) and low pass filter (LPF) track the frequencies of cross-overs 1 and 7 respectively. These filters are useful in trimming the input signal frequency range and removing unwanted signal.

It’s a Snap

The large number of bands can make operating the ML8000 difficult. Fortunately the Snap feature can instantly set all the Multi-band Limiter thresholds to current signal levels, for quick setup and adjustment of all bands. Instead of moving all the multi-band thresholds individually, simply press the ‘SNAP’ button – just to the right of the Multi-band Limiter enable control – and all the thresholds are updated. It’s literally, a snap!

The Snap feature is also useful when auditioning presets. Not every preset is best suited for every application, but the Snap feature can update the threshold (output ceiling) settings to current input levels, and thereby allow the user to see if the preset is a good fit.

Limiter Knee and Mode

ml8k_kneeThe ML8000 Master Limiter offers unique Character Mode and Knee controls for processing alternatives, for both the Multi-band and Master Limiters, making the ML8000 useful for a variety of applications.

The Knee control increases the transition between ‘unlimited’ and ‘limited’ signal peaks and creates a wider, nearly compressor-like response, while still preventing signal levels from exceeding the selected output ceiling. A Knee value of 0% is a standard ‘hard knee’ limiter. Increasing the Knee values causes the limiter to preserve more signal dynamics while keeping peaks below the selected maximum (output ceiling).

The Character Mode control effects how the stages of peak detection interact. Note the effect of the Character Mode control is most audible when the Release time is less than 200 msec, and even more noticeable for Release times less than 20 msec. As the Character Mode names imply, they balance the trade off between perceived loudness and audible distortion. Modes like ‘Soft’ and ‘Clean’ give a more pure result, while ‘Loud’ and ‘Crush’ give a more aggressive result.

Focus

ml8k_bandThe Multi-band Limiter has an additional option called Focus. The Focus modes determine how each band of the Multi-band Limiter tracks and responds to the input signal. The Focus modes are:

• FIXED – standard active processing
• VARI-1 – slightly narrower active processing ‘bell shape’ in each band
• VARI-2 – narrowest active processing ‘bell shape’ in each band

Note that in the VARI-2 Focus mode, a portion of the ‘bell peak’ is preserved by limiter processing, and can be observed during aggressive limiting of a particular band.

It’s a Wrap (Snap?)

The ML8000 Advanced Limiter has plenty of options to keep an audio engineer busy. And options are good! It’s a competitive field, and having the right tools for the job can make all the difference. Hopefully the ML8000 will find its way into your audio tool kit!

Demos are available 24/7 at mcdsp.com. Click here to request one today!

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