Fairlight CMI IIx - Page 4 - Harmonic Profiles

Page 4 of the Fairlight is all about Additive Synthesis.
To access page 4 type
P4<return>

To access page 4 help type
H4<return>
To step through the help pages use the ADD & SUB buttons on the keyboard 


The manual introduces this page as:
 "offering facilities for rapid additive sine-wave Fourier synthesis by
harmonic amplitude manipulation."

Here is an example of a page 4 display

 Page 4 (and page 5) permit the drawing of 32 sine wave harmonic amplitude envelopes, duration envelopes, and master volume envelopes.
The harmonic envelope is similar in concept to a ADSR envelope you will find on many synthesizers.

The loop feature means that any part of the overall waveform can be made to loop (sustain).
After you draw your waveforms, the CMI will process the data and yield the final waveform by the COMPUTE command. (use either the lightpen or the alpha numeric keyboard).

Here is the first HELP sheet for page 4

There are many forms of synthesis.
Most of us are familar with subtractive synthesis where you start off with a waveform that is rich in harmonics such as a square-wave and you subtract harmonics using devices such as filters.

Additive synthesis does the reverse. You start off with the simplest building block of sound , the sine wave & you add more harmonics. In theory, you can construct any waveform using just simple sine waves.

The mathematician Joseph Fourier first proposed this theory back in the 19th century.
The concepts of additive synthesis had also existed with the invention of the organ. This instrument uses different pipes of varying pitch. These can be combined to create very complex sounds & timbres.

The harmonic series works like this:
If harmonic 1 = fundamental pitch.(FP)
Harmonic 2 = FP x 2 = harmonic 1 x 2
Harmonic 3 = FP x 3. etc etc

You need to add lots of sine-waves to produce waveforms that closely approximates idealised mathematical forms. So maybe this method isn't the best for this.
The strength of additive synthesis lies in the fact that you can exert control over every partial component of our sound. This can produce some very intricate and wonderful results.

MODES

Page 4 has 2 modes:
Mode 1 & Mode 4.
The type of sounds you want to make will help you choose which mode to use.

In Mode 1 each vertical division represents 1 waveform segment
This means there are 32 waveform segments.
Each segment in turn is sustained according to the DURATION profile position of the segment.
During this time, the amplitude is modulated according to the slope of the ENERGY profle.
It's good for doing harmonic synthesis & generating "electronic" sounds. (pages 4 & 5)

In Mode 4 each vertical division represents 4 waveform segments.
(I guess this is why its called mode 4)
This means there are 128 waveform segments.
Each segment is played once before moving to the next segment.
This is more aimed at drawing & sampling. The manual suggests it be used when making "natural sounds" .
(pages 6 & 8)

 The numbers 1 to 32 are actually lightpen switches to display all 32 waveforms. However, if this is done the display can look confusing, so its possible to hide the display of some of the waveforms (they will still remain active, and will contribute to the final sound).

To set the mode of a voice you need to use page 3.
Here is a typical page 3

Use the arrow key to tab to MODE for the desired voice.
Type: n<set>
n = 1 or 4

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Wave Table Voice Facility

This option allows you to use waveforms other sine waves for additive synthesis.
Waveform segments from another loaded voice can be the source of the sound.

Harmonic numbers, now become segment numbers. You can't however select the current voice as a wave table.

In order to use this voice facility you need to load a voice into the system's memory first.
This is done in page 3.  After you have done this, you will need to select in within page 4.

To select any loaded voice for display & modification (within page 4) type:

V,filename<return>      or               V,n<return>

where filename  = the name of the loaded voice.
                      n  = the number 1-8 of a loaded voice.

The name, number, and mode of the current voice are shown in the upper right corner of the page.
The names and numbers of all loaded voices are shown on page 3 & page 7.

 
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This page is constantly being updated as I explore the Fairlight system.
If you have a Fairlight, don't hesitate to let me know if there are any mistakes or omissions.

 To be continued...................

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