CAM4: NR-4™

When quality is the defining criterion


The Problem

Traditional noise reduction methods are inadequate. Dual-ended processes require encoding and do nothing to remove noise already present in a signal. Low-pass filters remove as much wanted signal as noise. Dynamic filters pump, round off transients and dull the genuine signal. Gates remove no noise when open. Expanders pump, and multi-band expanders have poor separation filters, leading to loss of high frequencies, loss of ambience, and degradation of hard transients.

What's more, it's impossible to remove all the noise from a signal and leave the desired (genuine) signal completely unaffected. Consequently, the best you can hope for when de-noising material is a compromise that reduces the noise to an acceptable level while leaving the desired signal as unaffected as possible.

The Solution

CEDAR Audio developed NR-4 to remove as much unwanted noise as possible, and to provide as many options as possible that remove noise and restore the genuine signal to each userĀ¹s requirements. Consequently, it provides a simple but powerful interface that allows you to reduce the noise in many different ways, and is equally applicable to CD remastering, film soundtrack restoration, post-production, and forensic audio investigation.

The key to NR-4 lies our attention to detail, enabling us to improve almost every aspect of its performance. It is easier to use, more flexible, and it sounds better than any previous broadband noise reduction system. When absolute quality is the defining criterion, NR-4 is the only solution.

The Noise Fingerprint

Although it is impossible to know the precise amount of noise at each frequency at every moment, an accurate fingerprint is a useful tool, and can help to define the amount of noise removed by the system. Should it be difficult to capture a sample of noise, or if you have caught a small amount of signal as well, you can edit a Fingerprint or create one manually using the NR-4 drawing tools. These provide powerful opportunities to achieve the best possible results, especially when used with the integrated Spectrum Analyser, which helps you to create or edit a Fingerprint that most closely resembles the contour of the noise spectrum.

The Noise Reduction EQ

The Noise Reduction EQ re-shapes the noise content contained in the input signal. Typically, you will want to concentrate the noise reduction in the range where the hiss is most intrusive, while leaving other areas relatively untouched. This is very different from lesser systems that attenuate the noise content equally at all frequencies.

The Noise Free EQ™

Although capable of acting like a conventional parametric equaliser, the Noise Free EQ™ is a mastering quality EQ that acts only upon that part of the signal identified as genuine signal. You can say, therefore, that it is like a filter that shapes only the true signal content of the input signal. Common uses for this include mild boosting of high frequencies to counteract any loss of perceived brightness caused by the noise reduction itself.

Modelling & Brightness

The three modelling options control the behaviour of the NR-4 algorithm. The audible differences between these models can be very subtle depending on the nature of the signal and noise. The Brightness control gives you some flexibility to determine the nature of the dehissed sound, balancing the amount of noise reduction with the risks of side-effects.

NR-4 offers many other facilties that help you to achieve the best possible results from the source material. Like many other CEDAR Cambridge modules, it provides zooming and Markers, multiple levels of Undo and Redo, and it is fully automated using the Timecode Automation Controller, the Event Manager and the File Processor.

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