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CEDAR Cambridge Utilities

The DC Filter

Removing DC offsets

DC Filter

The DC Filter is a core module provided on every CEDAR Cambridge system.

It offers a roll-off of 12dB/octave at any user-defined frequency in the range 1Hz - 20Hz and, because removing DC offsets improves the signal modelling used elsewhere in CEDAR Cambridge, it is invaluable when used before restoration modules such as Declickle-2, Vintage Decrackle, Auto Dehiss, and NR-4. It also increases signal headroom, and allows you to apply higher gains to output signals if desired.

Users may place the DC Filter anywhere in the signal chain, and can determine which channels are affected by the filter. A convenient display indicates the magnitude of any DC offset identified and (if desired) removed by the system.

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CAM1: Spectrum Analyser

An audio spectrum analyser with 0.02Hz accuracy

CAM1: Spectrum Analyser

The Problem

Most audio workstations use FFT spectrum analysers. With frequency bins of equal width (whether at the upper or lower end of the spectrum) these suffer from very poor resolution, especially at low frequencies, and they are not suitable for serious audio analysis. For example, an analyser with 1,000 bins operating at 96kHz will have a resolution of, at best, 96Hz. This is more than two octaves at bass frequencies, and is entirely useless for observing low frequency signals or degradations such as hums and buzzes.

The Solution

The CEDAR Cambridge Spectrum Analyser is not an FFT analyser; it is more akin to the analysers found in electronic design laboratories, and it offers a superb resolution of 0.02Hz. This is approximately 5,000 times more accurate than the FFT analyser described above.

The Spectrum Analyser allows you to display the data in four ways that dramatically enhance is usefulness when performing noise reduction, debuzzing, and other restoration tasks.

  • Normal mode - a free-running analyser
  • Averaging modes - Display the average amplitude at each frequency from the moment that you select the mode until you cancel it
  • Maximum mode - Displays the peak value at each frequency, calculated from the moment that you select this mode until you cancel it
  • Minimum mode - Holds the minimum value at each frequency, calculated from the moment that you select this mode until you cancel it

With additional facilities such as Select and Zoom, the ability to measure the difference in gain and frequency between two points on the screen, linear and logarithmic displays, and CEDAR's unique Markers that let you transfer frequency information between CEDAR Cambridge processes, the CEDAR Cambridge Spectrum Analyser is the most advanced and most useful tool of its type.

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Dither and Noise Shaping

Applying Dithering and Advanced Noise Shaping

 Dither

The wordlength within CEDAR Cambridge is 64-bit floating-point. You may select the output wordlength to be 8, 16, 18, 20, or 24 bits.

Dither

Dither is required when you wish to reduce the number of bits used to represent a signal. It minimises the distortion introduced by truncation, reveals more low-level information, and creates a more pleasing audio signal.

Dither Source

CEDAR Cambridge provides three dither source options that allow you to apply the most suitable dither for each piece of audio.

Noise Shaping

Noise shaping allows you to move the noise introduced by dithering to less obtrusive (i.e. higher frequency) areas of the audio spectrum. CEDAR Cambridge provides five noise shaping options.

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2 Channel Tools

A general toolkit for monitoring and adjusting 2-channel signals within CEDAR Cambridge™

CEDAR Cambridge 2 Channel Tools

The 2 Channel Tools provide a toolkit for monitoring and manipulating stereo signals within CEDAR Cambridge. You can apply the meters and tools to any two channels from the eight provided by the system.

Lissajous and Balance metering

The graphic display provides a Lissajous figure plus a balance meter with a range of 30dB in either direction.

Balance

Allows you to specify the gain differential between the two channels.

Auto Balance

Maintains the balance of the channels such that the output signal remains centred.

Output Modes

Normal, Mono sum, Mono difference.

MS Encode and decode

Creates an M-S pair with output channel A carrying the A+B signal, and output channel B carrying the A-B signal. You can invoke two instances of the tools with processing modules lying between them to generate a wide range of M-S effects such as stereo width enhancement.

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Metering

A multi-channel metering module that can display up to eight channels simultaneously

CEDAR Cambridge Metering

The CEDAR Cambridge Metering module provides simultaneous amplitude metering of all channels selected in the Channel Selector. It provides four items of information for each channel: 

  • RMS Metering
  • Peak Metering
  • Peak Hold with a hold time of one second
  • Peak Hold from the most recent reset 

The Metering module conforms to BS6840: Part 18: 1996 and to IEC-60268-18

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The Gain Module

Applying Gain, Solos and Mutes

The Gain Module

CEDAR Cambridge provides a dedicated Gain module that allows you to apply gain independently to each channel. You can use one or more instances of this module as an input gain control, as a makeup gain, or you can place it at any other point(s) you desire in the processing chain.

Each instance of the Gain module allows you to mute and solo in place any tracks that you wish, or to solo a single track to all.

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