RTW Continuous Loudness Control

Software delivers real-time processing for program regulation
RTW’s software conforms to a variety of standards, including EBU R128, ATSC A/85 and TR-B32.

We all have experienced watching TV when a commercial break starts and you lunge for the remote because audio for the commercial is way louder than the program you were watching. That happens because the program has a wide dynamic range, while the commercial is compressed. They may have the same peak level, but the compressed audio is perceived as louder.

Several years ago, in an effort to solve this irritating issue, the International Telecommunications Union developed a new audio scale known as LKFS (Loudness K-weighted relative to Full Scale), which employs a K-weighted filter to yield measurements reflecting how loud a person perceives a given passage of audio. The European Broadcast Union calls this measurement LUFS (Loudness Units Full Scale).

Concurrently, the EBU developed a set of rules defining maximum audio levels for broadcast based on this scale; in 2012 Congress approved the CALM Act establishing similar rules for broadcast in the United States. These standards define average loudness for broadcast in Europe (-23 LUFS) and the U.S. (-24 LUFS). If your audio exceeds this average level, it will be turned down to the requisite level upon broadcast.


RTW’s Continuous Loudness Control software is designed to regulate program loudness to conform to a variety of broadcast standards for average loudness, including EBU R128 (Europe), ATSC A/85 (U.S.) and TR-B32 (Japan). Using a proprietary look-ahead algorithm developed in conjunction with the IRT (Institut für Rundfunktechnik; also known as the Broadcast Technology Institute in Munich), CLC can process live audio or files to a “target” loudness level with or without altering the original Loudness Range (LRA). CLC runs under Mac or Windows and can be used stand-alone or as a plug-in for most DAWs. CLC’s unique algorithm “learns” a program’s dynamic character and predicts subsequent levels, enabling the software to operate in real time as well as offline.

I ran CLC on my Mac Pro as a stand-alone application and also as a plug-in for Digital Performer and Pro Tools. Installation was easy, though it requires the use of an iLok. CLC’s main window shows Input and Output values for Integrated Loudness, Loudness Range, Short Term Max, Momentary Max and True Peak levels. The Loudness Controller graph on the left shows the relationship between loudness input and output, while the LRA Controller graph on the right displays the relationship between Loudness Range input and output. The center section features a Loudness Gain bar graph, an LRA reduction bar graph and an activity indicator for the True Peak limiter. I found the bar graphs and TP indicator extremely useful in evaluating the software’s influence on processed audio. RTW presumes that the user has familiarity with Loudness Units, so you won’t find any tutorial information regarding LUFS, LU or LRA in the manual.

CLC processes audio in three distinct modes. Dynamic mode uses RTW’s proprietary time-variable processing of loudness and loudness range, with target values for each. Static mode simply shifts the gain level up or down but leaves the dynamics unchanged unless you decide otherwise. Semi-dynamic mode functions somewhat like a traditional compressor, permitting dynamics to be reduced by a percentage (it would be nice if we could see that value as a ratio).

My first use of CLC was to process audio for a 60-second commercial spot with background music and a voice-over. I plugged CRC into the master channel of a Digital Performer session and pulled up a preset for ATSC A/85. Opening up the CLC menu revealed some of the process settings, most noticeably Target Loudness and Maximum LRA.

The ATSC A/85 preset targets audio to -24 LUFS and allows a loudness range of 12 LU. This worked very well in managing the overall loudness, but we felt that the music before and after the voice-over was slightly low. Setting the Max LRA to 8 LU solved the issue, raising the perceived loudness of the music while maintaining the target output level. The same settings worked perfectly on a radio spot for a local NPR station. All the while, the sound quality remained largely unchanged—though at severe settings it was possible to create artifacts such as pumping.

Next up was using CLC as a stand-alone application for file, batch and live processing capabilities. When you open CLC as a stand-alone app, the software defaults to Device mode, the purpose of which is to process audio live via your audio interface. This is the mode where CLC flexes its unique muscle (see the “Try This” sidebar).

Playback mode permits CLC to import a file and process it to a target loudness level. This is not a “playlist function”—it’s intended as a way to preview the effects of CLC and adjust settings if needed. I found this to be a useful way to audition and tweak settings for Device mode. I could import a test file, apply CLC in Playback mode, make adjustments if necessary, and then save my settings as a custom preset. Then in Device mode, I could load that custom preset and apply it to live streamed audio.

In File mode, CLC imports an audio file, analyzes it and then creates a loudness-corrected version. Results in this mode on a Mozart piece were fantastic: I was able to set a target of -18 LUFS, correct the Integrated Loudness within a half-LU and tame the LRA within 0.2 of 12—and the audio didn’t sound processed at all. Impressive.

I also used File mode to create a preset for processing a series of show cues, the levels of which varied all over the place and required a fair amount of babysitting on the mixing desk during a live show. Batch mode allowed me to load in all of the files (CLC reads just about any file format), then analyze and process them into a new folder. The original files remained unchanged. I chose to write the corrected versions as WAV files, but you have the option of maintaining the original file format or converting to any of several formats, including BWF, FLAC or AIFF. I was then able to burn the loudness-corrected files to a CD for playback during the show. The levels between cues were way more consistent than when using the original files.


Continuous Loudness Control is a very powerful tool squarely aimed at the broadcast market, but really any studio that creates audio for broadcast would find it indispensable. It can be used to correct audio that was mixed without consideration for broadcast loudness standards, as well as for targeting a loudness standard while a production is still in progress. RTW’s presets are incredibly useful, and I found myself relying upon them more often that trying to DIY settings. As far as we know, CLC is the only software able to perform loudness correction in real time with minimal latency, making it invaluable for live streaming on TV, radio, the Internet or even in corporate applications.


PRODUCT: CLC Continuous Loudness Control
PRICE: $899.99 MSRP
PROS: Operates as a plug-in or stand-alone in real time; accommodates a variety of international broadcast loudness standards; provides live, file-based and playback modes
CONS: Not for the casual user. Manual needs a better translation.


RTW’s Continuous Loudness Control has the ability to process audio to a target loudness level in real time. First, click the Device tab in the main window and then click on the tool icon to open the Settings page. Clicking on the Audio tab will enable you to set the number of I/O channels and the channel mode (Stereo, 3.0, 5.0 or 5.1). Under Device Setup, set CLC to the audio interface you’d like to use. You can then set the number of active inputs and outputs (as defined by your interface), sample rate from 44.1 to 192 kHz, and buffer size from 0.4 to 45 mS. Click OK to accept the settings and close the Settings page. CLC will now stream audio through your interface from an external source such as a mixer, with the output being loudness-corrected.

Steve La Cerra is a New York-based audio and live sound engineer.

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