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CEDAR Cambridge Restoration Modules

CAM3/A: Auto Dehiss

Automatic dehissing that works

CAM3/A: Auto Dehiss

The problem

In the past, digital dehissers that used no fingerprinting or noise reduction profiling were prone to side-effects known variously as twittering and glugging. On earlier CEDAR processes, it was possible to avoid these unwanted sounds by careful and judicious use of the controls, but it has never been possible - until now - to remove broadband noise correctly with almost no user intervention.

The solution

Auto Dehiss embodies a more advanced algorithm than any previous dehisser. It offers significantly improved performance and has a unique Auto mode that enables the software to determine the broadband noise content, removing this without the introduction of unwanted side-effects or artefacts.

We have even retained a manual mode that allows you to control all parameters and fine-tune the noise reduction.

The Plaudits

CEDAR's original DH-1 Declicker - the world's first mastering quality digital dehisser that did not require a noise fingerprint - was voted Best Of Show by the editors and readers of EQ Magazine.

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CAM4: NR-4™

When quality is the defining criterion

CAM4: NR4

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 user¹s 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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CAM18: NR-5

Incomparable noise reduction for CEDAR Cambridge

CAM18: NR5

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

Building upon the latest noise reduction algorithm developed for the rackmount CEDAR Duo™ DDH Auto Dehisser and the Auto Dehiss process already available on CEDAR Cambridge, NR-5 marries our best signal processing with numerous facilities that help you to achieve the best possible results. It will work equally well with or without a noise fingerprint, and an array of tools allow you to manipulate the noise identification and reduction profiles in ways that are unique to CEDAR's flagship products.

To make NR-5 as quick to use and intuitive as possible, and to eliminate any learning curve for users of our previous noise reduction flagship, we have retained the style and layout of NR-4™. However, the clear screens and easily mastered controls of NR-5 belie the increased capabilities of the underlying algorithm, which removes more noise than ever before with even fewer side-effects or artefacts.

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-5 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.

NR-5 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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CAM6: Declickle 2

What else would you call something that removes all traces of clicks and crackle?

CAM6: Declickle 2

The Problem

CEDAR invented real-time digital declicking and decrackling, demonstrating them to amazed audiences at the 89th AES Convention. However, these earliest digital declickers and decracklers suffered from a limitation; while they removed impulsive noises from the majority of material, they could damage the sounds of brass instruments, solo violins and singing, and all declickers based on the techniques revealed by CEDAR's original research still suffer from it.

The Solution

Declickle 2 embodies new technology, offering better impulsive noise detection and a better interpolator than any previous declicker or decrackler. This results in superior performance across a wider range of material than ever before. Indeed, this performance is so good that, in almost all cases, it is not possible to hear that the signal was damaged prior to restoration.

 

Why Declickle 2?

Unlike a standard declicker, Declickle 2 is able to detect high densities of low amplitude, short duration disturbances within the signal. However, removing each of these unwanted impulses using a basic interpolator would not be satisfactory because of their fundamental nature. Standard algorithms assume that a click or scratch has totally corrupted the audio and that there is no useful information about the wanted signal during the click. Since the disruptions that cause crackle are very small they may be considered to be additive, and this assumption is no longer appropriate. Declicking a crackly signal discards a lot of useful information that an optimal algorithm can use to improve the quality of the processed audio.

Despite the power of Declickle 2, its user-interface is extremely easy and quick to use, and is suitable for users with limited audio engineering experience.

The Plaudits

CEDAR's DC-1, DCX and DDH declickers are acclaimed throughout the audio industry and our 96kHz software declicker won a SSAIRA Award as the best plug-in of the year.

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CAM6: Vintage Decrackle

Revitalising a classic audio restoration process

CAM6: Vintage Decrackle

The Problem

Conventional declick processes are unable to identify and eliminate low level crackle without eating into the genuine audio. If misused in this way, they will damage the ambience and remove genuine musical transients.

The Solution

Vintage Decrackle is based upon an enhanced implementation of our Split & Recombine algorithm. This proved to the world that real-time decrackling was not only possible, but could be performed to the highest remastering standards.

Manual mode

In manual mode, Vintage Decrackle offers the same performance as our award-winning CR-1 Decrackler and boasts a remarkable ability to dig deep into a damaged signal to identify and remove all manner of ground-in and grungy crackle without damaging the wanted audio.

Auto mode

In auto mode, Vintage Decrackle automatically determines the optimum settings and in many cases yields superior results to setting the parameters by hand. This improves productivity and the quality of the processed audio.

Vintage Decrackle also removes many forms of buzz and some amplitude distortions from material as diverse as cylinder recordings and live broadcasts contaminated with lighting buzz.

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CAM7: Debuzz-3

Eliminate buzzes and hum for professional audio and forensic use

CAM7: Debuzz-3

The Problem

The family of degradations known as buzz includes many audio phenomena that are characterised by having a large number of strong, closely spaced harmonics. Traditional comb filters will remove these buzzes, but the side effects of echo and a strongly coloured hollow nature are unacceptable. Alternatively you could use a cascade of high-Q parametric filters, but the number of harmonics generally makes the setup time impractical. Furthermore, these traditional techniques cannot adapt to variations in the buzz fundamental frequency and they will always damage any signal that coincides with the buzz harmonic frequencies.

The Solution

The Debuzz-3, algorithm is our best yet. It provides full-bandwidth processing, removing components across the entire audio spectrum, and it is capable of removing all manner of buzzes and hums with fundamental frequencies as high as 500Hz. Compared with earlier algorithms, it offers improved signal modelling and better component tracking. Having locked on to the fundamental, it even has the ability to cope with jittery buzzes. Typically, Debuzz-3 will successfully remove the buzz even if the frequency drifts by as much as 2% at 50Hz at 44.1kHz sample rate.

The module also rescues signal that lies at the same frequencies as the buzz harmonics. It does this by analysing the dynamics of the signal and buzz, optimally detecting and reducing the buzz with minimal side effects. What's more, the Odd Harmonics option (introduced in CEDAR Cambridge V9) eliminates processing at the even harmonic frequencies. This ensures that no unnecessary processing occurs if the buzz comprises predominantly (or only) odd harmonics, resulting in even less chance of damage to the genuine signal.

With controls to limit the processing bandwidth (and therefore improve selectivity), to limit detection and/or processing to the channels of your choosing, and to control the detector and amount of buzz removed, Debuzz-3 is a remarkably powerful tool. There's even a confidence meter that allows the system to tell you whether the chosen frequency is, in fact, the true fundamental of the buzz or hum. What's more, Debuzz-3 also takes advantage of CEDAR's unique Markers that let you transfer frequency information between CEDAR Cambridge processes. This is of huge benefit when using the Spectrum Analyser (with its 0.02Hz resolution) to detect unwanted fundamentals and their harmonics.

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CAM8: Declip

Eliminating clipping from overloaded audio

CAM8: Declip

The Problem

Clipping occurs when a piece of equipment or a medium carrying a signal is unable to handle a high level presented at its input, and will usually be heard as a harsh distortion that increases in intensity as the clipping becomes heavier. In all cases of clipping, it is the portions of the waveform near its extremities that are affected, while portions of the waveform closer to zero are unaffected. Examples of clipping include:

 

  • Digital clipping
    The signal contains many false samples. Viewing the audio waveform would reveal 'flat tops', at which points the genuine signal is destroyed and replaced by false samples at the maximum amplitude.

  • Clipping of analogue equipment and media
    There are many different types of analogue clipping. These will usually be less obvious than digital clipping, with the hard edges visible in the former case replaced by a more rounded profile.

     

The Solution

Declip is a genuine declipping algorithm that allows you to identify and remove most instances of clipping in a single real-time pass. It does so by presenting a visual indication of the density of sample values in the signal. If the Signal Analysis window displays 'hard' vertical edges, this demonstrates that the signal has been clipped at that sample value. It is then simple to remove the offending samples and reconstruct the signal. If you wish to inspect a region of the display more closely, you can use zoom to increase the resolution, allowing you to see finer detail within the signal. Furthermore, like the CEDAR Cambridge Spectrum Analyser, Declip offers multiple display modes that help you to analyse the audio correctly.

Two processing modes are provided, and these allow you to choose between an algorithm optimised for light clipping, and one optimised for heavy amounts of clipping. This ensures that you remove the problem without causing damage to the genuine signal. But be careful... the amplitude of a declipped signal can be significantly greater than that of the original.

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CAM9: Phase Corrector

Eliminating timing errors and the resulting audio degradations

CAM9: Phase Corrector

The Problem

Timing errors can occur whenever multiple signal paths are inconsistent with each other. The resulting distortion of the phase relationships between the signals and the consequent filtering effect cause many problems including loss of high frequencies, muddy bass, poor mono compatibility, and a general smearing of the image. Worse still, if the timing error is not constant, you can hear a flanging effect.

Audio engineers have traditionally employed a range of processors to hide these deficiencies: equalisers, stereo enhancers, dynamics processors and reverb units. However, none of these attack the heart of the problem - the small but significant timing errors between the channels.

The Solution

The Phase Corrector corrects these problems not by masking them, but by eliminating them. It does this by identifying any monophonic component(s) common to a reference channel and the channel(s) being corrected, and then measuring the timing differences between them. If any such errors are detected, the system recreates the signals so that they are accurately aligned. It will track any changes in the error, dynamically updating the amount of correction it applies at any given moment. A manual mode allows you to shift a signal by as little as 0.01 samples - an offset of just 0.1 microseconds at 96kHz.

A sophisticated filter minimises the chance that the detector will be fooled by unusual signals that contain little or no monophonic components, so that CEDAR Cambridge should never generate false corrections and introduce phase/time errors of its own.

The Phase Corrector allows you to select which tracks are shifted automatically, which are shifted manually, and which (if any) are left unaffected. You can select any channel to be the Master Channel, and the module will calculate the independent timing errors of all the others, thus allowing you to lock-up the imaging for multitrack, 5.1 and 7.1 material.

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