World Class Restoration Tools
An outline of the CEDAR
"Computer Enhanced Digital Audio Restoration" system


Many people have heard the name CEDAR in relation to Audio Restoration, but don't really know what it is or exactly what it does.

CEDAR is an acronym (one of those "made-up" words) that stands for

Computer Enhanced Digital Audio Restoration.

It found its beginnings in 1986 at England's University of Cambridge when the National Sound Archive approached the Signal Processing Laboratory at Cambridge with a requirement to "clean up" recorded material in the Archive before it had deteriorated to the point of being useless.

It took a few more years and a few breakthroughs in digital design for CEDAR to arrive at the stand alone modules that make up the backbone of the CEDAR equipment today. The earlier designs are supplanted by a "series 2" design that further improved on the original, and utilizes two floating point DSP (Digital Signal Processing) to do the internal processing at an impressive 40 bit resolution!

There are four CEDAR stand alone rack mount modules, each of which occupies 3-1/2 inches of rack space, and operates in "real time"... that is, feed dirty audio in, and get specifically processed clean audio out, all in the amount of time it takes to play the material. Each box is stereo in nature, having two completely independent channels of real-time processing.

CEDAR DC-1 module

DC-1 De-Clicker

CEDAR CR-1 module

CR-1 De-Crackler

CEDAR DH-2 module

DH-2 De-Hisser

CEDAR AZ-1 module

AZ-1 Azimuth Corrector

The four CEDAR rack mount modules look similar at a glance, and only a closer look at the blue operating screen or the label on the front panel will tell them apart.

The DC-1 De-Clicker

Is the most important module, it removes the normal clicks and pops that we are all familiar with, but also works on what most people would call "crackle", which is really hundreds of very small clicks in close proximity. The DC-1 running on the LARGE algorithm will miss smaller clicks, but also, if not set up properly will take the tops off muted trumpets, trombones and some (notably male) voices. Under these conditions, two passes are usually necessary for best results, one under the LARGE algorithm and another under the SMALL algorithm. The hand that guides the process must make a variety of judgements along the way to better sound. The DC-1 is capable of performing 50 million floating point calculations per second which translates into removing up to 2,500 scratches or clicks per second, per channel.

The CR-1 De-Crackler

Removes what the DC-1 doesn't get, mostly low level surface imperfections, and some distortions due to groove damage. The DC-1 and CR-1 have a great degree of overlap in what they do, and the DC-1 De-Clicker gets what most people would think of as "crackle"... BUT, the CR-1 De-Crackler will accurately differentiate between crackle, buzz, some distortions and the genuine signal, and will gently remove imperfections that the DC-1 won't touch without leaving undesirable artifacts.

The DH-2 De-Hisser

Is the improved version of the original DH-1. Without any need for a spectral "fingerprint", it is most effective on broadband noise such as tape hiss but also attacks the residual hiss noise of phonograph records after the above DC-1 and CR-1 module(s) are applied.

The AZ-1 Azimuth Corrector

Phase problems and time delays between left and right channels of a stereo signal account for many of the problems suffered by audio professionals. Typical consequences include poor mono compatibility. poor stereo imaging and muddy bass response. The AZ-1 can correct phasing differences on stereo recordings that cause cancellations of frequencies when combining to mono. It has no effect on mono recordings at all, but can be used to do some processing before a mono phonograph recording, played in stereo, is summed to mono.

All of this comes with a hefty price tag...
in dollar terms, in the low five figure range per box.
(Your currency may vary!)

Computer Based Systems
A little history first...

In the beginning, there was an IBM PC computer based board and software that achieved the things that the above noted stand-alone modules do, and more, on a one-at-a-time basis, and they were known as the CEDAR PRODUCTION SYSTEM or "CEDAR-2". The software was modular and called:

Module 1 - Scratch Removal
Module 2 - Crackle Removal
Module 3 - Digital Equalization
Module 4 - Noise Reduction
Module 9 - Sample Rate Conversion
Module 11 - Phase/Time Correction

There was some confusion over CEDAR-2 and the "series 2" (Mk-2) versions of the stand alone boxes described above, but "series 2" is simply a new hardware platform with many improvements, and they use the same software algorithms, essentially producing the same end results.

CEDAR-20 replaced CEDAR-2, with its slightly renamed software modules, and an Auto De-Hiss module was added.

Module 1: Real-Time Scratch and Click Removal
Module 2: Real-Time Crackle Removal
Module 3: Disc Restoration
Module 4: Real-time IIR Equalisation
Module 5: 'Auto De-Hiss' Real-Time Noise Reduction
Module 6: 'Hiss-2' Real-time Noise Reduction
Module 11: Dynamics
Module 12: 'Phase-EX' Phase/Time Correction

Current CEDAR processes for the IBM PC computer...

CEDAR's latest offering is a range of individual real-time audio restoration modules that run under Windows 3.1 and Windows 95.

  • Up to eight simultaneous stereo restoration processes
  • Up to 16 simultaneous channels of De-Scratch, De-Crackle, De-Hiss or other CEDAR processes
  • Simple installation on all suitable PCs
  • Compatible with all leading PC-based audio editors

CEDAR for Windows combines key features of both CEDAR's stand-alone processing modules and the CEDAR 20 System, offering all the flexibility and expandability of a modular PC-based system with the simple interface and controls of CEDAR modules. CEDAR for Windows' processing cards and software require no complex installation procedures, and can be quickly and easily installed.

Up to eight 24-bit stereo ProDSP I/O boards can be installed in any PC with sufficient ISA slots, allowing up to eight simultaneous stereo restoration processes to be executed - in series, in parallel, or any combination of series or parallel processing.

The following real-time software modules are currently available:

WIN1 De-Click
WIN2 De-Crackle
WIN3 De-Hiss2
WIN4 NR-3 Noise Reduction and EQ
WIN5 Phase Correction
WIN6 De-Buzz

Additional processing modules based on the pioneering CEDAR-20 algorithms are in development, and on introduction will see "CEDAR for Windows" become the only current IBM PC CEDAR implementation.

All CEDAR for Windows processes are real-time, with 24-bit I/O and 40-bit floating-point processing.

WIN1 De-Click

Processing is controlled by a simple software panel offering Threshold and Gain controls, pre/post switching, and 3-position 'Scratch Model' selection.

WIN2 De-Crackle

A software control panel offers simple operation via only five controls: Threshold, Split Level, Gain, pre/post switching, and 'Crackle Model'.

WIN3 De-Hiss2

With just three simple de-hiss contols (Threshold, Hiss Attenuation, and Ambience), plus Gain and pre-post switching, on the software control panel, Auto De-Hiss is also one of the simplest mastering quality noise reduction packages.

WIN4 NR-3 Noise Reduction and EQ

A "fingerprint" noise reduction allowing taking a "sample" of the ambient noise to be removed. Much more elaborate but with results that are un-obtainable any other way.

WIN5 Phase Correction

The CEDAR for Windows version of the AZ-1 stand-alone functions.

WIN6 DeBuzz

This latest addition to the CEDAR for Windows software modules, provides a means to attack buzz noises that were previously difficult to deal with without affecting the desired program content.


Budget versions of the four main CEDAR stand alone modules, the De-Clicker, De-Crackler, De-Hisser and Azimuth Corrector have now become available along with a new device, De-Buzz. All are at a dollar cost in the mid-to-high four figure range. (Again, your currency may vary!)

Adjustments to CEDAR can be made noiselessly and "on-the-fly", which allows "scripting" the material to be processed to make adjustments to catch large disturbances and thus use minimal processing, resulting in a superior restoration result, and a desirable additional feature is it minimizes the time spent to process, and hence, the overall cost to the end client.

NOTE: Images used with permission of HHB Canada, the Canadian distributor of CEDAR




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