Three Compliance Metering Plug-ins

Apr 1, 2013 9:00 AM, Mix, By Brandon Hickey

Versatile Old/New-Style Preamp With EQ


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The NuGen ISL is designed to address another fundamental component of A/85 and R.128 compliance. For years, we have relied on peak limiters where a threshold is set at a certain decibel value, and the limiter is engaged if the value of a digital word, or “sample,” exceeds that threshold. The recent realization is that sample-accurate peak measurement doesn’t always tell the whole story. When D/A converters reconstruct the string of samples and turn them back into voltage, oversampling may occur, which essentially creates smooth curves between one sample and the next. In some cases, these newly created curves exceed the limiter threshold and will clip later down the line. In other cases these inter-sample peaks will clip during AAC, MP3 or AC-3 encoding. Traditional brick-wall limiters like the Waves L1 have no ability to predict this, and as a result, many engineers will just play it safe, lower the threshold and sacrifice headroom.

During the creation of the ITU-R BS.1770 loudness metering model, engineers also developed an algorithm to meter inter-sample peaks by oversampling within the metering software. When oversampled peaks are measured as opposed to sample-based peaks, the term True Peaks is applied, and quantified in dBTP. The A/85 spec demands that program material stays below -2 dBTP, while R.128 sets the ceiling at -1 dBTP. Measuring in terms of dBTP is also useful in the music world where mastering hot is a common practice, and hot masters can lead to clipped MP3s when limited with traditional limiters.

The NuGen ISL is a True Peak limiter, which means that it is a brick-wall limiter whose threshold is set in terms of dBTP rather than sample-based peaks. This makes it the perfect tool for broadcast and post-production, because you can set it and forget it and then rest assured that you will always stay compliant and never clip during encoding. Controls are very similar to what you would find on any brick-wall limiter, so it is easy to pick up. Large vertical bar-graph meters display input and output. A slider on the input meter sets the ceiling of the limiter (it can also be input numerically in a box found below this meter). The gain reduction is displayed on a set of meters in the middle of the plug-in. ISL can operate in mono, stereo or 5.1, and a Channel Link control, set in terms of percentage, determines whether the multiple channels will be limited individually, or how much bearing they will have on each other’s gain reduction.

In a deeper menu, there are settings to control the color scheme of the meters, which the user can break into four color bands. The decibel break points are user-selectable, and the color for each of those bands can be chosen from a large color palette. Momentary and maximum peak indicators can be engaged or disengaged selectively, and the meter decay ballistics can be chosen between instant, DIN or the Nordic ballistics. The meter’s routing is user-selectable between the Dolby/Film standard, the DTS standard, and the SMPTE order. Changing orders actually changes how information is routed into the plug-in, so, for example, channel 2 is always displayed on meter 2, but you can change whether that is labeled center or right.

A look-ahead setting allows the metering algorithm to respond to quicker transients and level them without error; however, reducing this setting can make the sound a little punchier. It is easy to compare the difference in settings using the “Listen Mode” controls. In “Difference” mode, you can listen exclusively to what information is being limited and make adjustments accordingly. A-B’ing this function on and off was very revealing when judging the look-ahead setting and the release control, which adjusts the time that it takes the limiter to return to a state of zero gain reduction.

Naturally, the original goal of the plug-in was to set a ceiling, have it tame the mix’s peaks, and not make it work too hard. When it was only reducing a few dB, it was essentially inaudible, as planned. What was really impressive, though, was that I could dig deep, reducing gain significantly, and still the plug-in stayed incredibly clean. Just to see how far I could go before I heard negative effects, I would play with throttling the input gain and scaling back the output ceiling, and even with 30 dB of gain reduction, quick-transient sounds like machine guns still maintained a clean, usable sound. Pushing beyond that, things started to sound distorted, but the sound was much more like analog distortion than I was used to hearing from a plug-in.

With the ISL’s ability to prevent True Peak overloads, and the only rival product being Flux’s Elixer, it’s hard to imagine the ISL won’t catch the attention of many broadcast engineers. The sound, however, is what I found the most striking. I would be inclined to use it over the Waves L1 in post-production situations for the True Peak limiting, but even in music mixing or mastering for its ability to get loud very cleanly. Performance was smooth without ever glitching, CPU usage was reasonably efficient, and in a 24-bit, 48kHz Pro Tools session, it only imparted 64 samples of delay on the master fader.

Brandon T. Hickey is a freelance engineer and audio educator.

NuGen Audio

Product: ISL

Website: Price: $249 direct

Pros: Easy to use. Sounds fantastic.

Cons: 5.1 max, no 7.1 or higher yet.

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