Monday 21 October 2019

Yamaha DX7 - Operators & Algorithms

Some notes on using the DX 7.
Yamaha released the DX7 Mk1 in 1983.
I only just bought a Mark 1 about a week ago so there is a steep learning curve ahead.

These will be added to over time and hopefully help me to master FM synthesis.


FM synthesis was first developed by John Chowning in 1967 at Stanford Uni, then licensed to yamaha in 1973.it's very different to Subtractive synthesis. There are no VCOs, VCFs or VCAs..

It's kind of the opposite of a subtractive synth.
In a subtractive synth you start with harmonically rich wave forms like Saw, Square, etc. and you use filters to subtract those harsh frequencies... to smooth the sound out a bit.
In FM synthesis, you start with a sine wave and you then use other sine waves to distort it to create new
tones

Instead of the VCO, FM uses an operator.
This generates a sine wave.

The DX 7 has 6 sine wave operators
Operators are actually more than just oscillators.
They can be viewed as a package containing an oscillator, an amplifier & an envelope Generator.
The operators can be either a carrier or modulator.

Carrier - this controls the sound output.
Modulator - controls the harmonic content of a sound. It determines the shape of the waveform produced and therefore its timbre

By rearranging the operators, we can generate harmonically rich tones.
These arrangements are known as ALGORITHMs (there are 32 of these).

The operators on the bottom row of each algorithm are sound producing carriers. The ones above are modulators.


Algorithims determine how the 6 operators interact with each other.
There are 32 algorthims.
Picking the correct algorithm is the key to creating a patch.
Each algorithm is suited to a particular type of sound.

For example to make a:
Pad or texture sound.. ---- something complex with layers, ....we need something with multiple sounding operators or carriers.
To make a Bass or lead sound -- we might use an algorithm with less sound producing operators and more modulators.

The algorthims are divided into subgroubs that have similar structures.
(Stacking, Branching, Rooting and Carrier-only)
These groups, will help you to understand how they interact and their sounds

Group 1  - algorthms 1, 2,3, 4, 5, 6.

These are stacked algorithms.
2 to 4 operators.
2 towers to 3 towers.
Between these towers there is no frequency modulation. Instead they are added ... ie they are an example of Additive Synthesis.
These types pf algorthims are used for such things as
Strings ( A4 STRINGS ALG 2),
Piano ( A11E.PIANO 1 ALG 5).
Tubular Bells ( A26 TUB BELLS ALG 5).

Algorithm 2 consists of 2 independent towers with operators stacked on top of one another.
 gREAT for sounds with high harmonics like strings .
Notice also the feedback loop. You can control the amt of feedback by its Level & Output Level.
We use feedback operators to generate higher harmonically rich tones such as sawtooth waves.

We can also adjust the Frequency Ratio of each operator to generate particular harmonics.
The frequency relationships between modulators and carriers are very important.


+ A ratio of 1:1 (ie. equal frequencies) tend to produce a waveform roughly equivalent to a sawtooth.
If Operator 2 = 1.00
     Operator 1 = 1.00
we will generate a sawtooth sound

+ A ratio of 2:1 (modulator 2x the fundamental frequency) would produce
something more square-like. As you increase the ratio you will get more high-end fizz.
So if we change the ratio like so:
Operator 2 = 2.00
Operator 1 = 1.00
we will generate a square wave

If we change the ratio like so:( where the modulator was a non-integer multiple of the carrier)
Operator 2 =3.50
Operator 1 = 1.00
we will generate a metallic or a Bell Tone (in-harmonic tone)

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Algorithm 5 is a bit more complex.
We have 3 independent towers with two operator stacking. This is great for bell & electric piano sounds.
In a DX7 with 6 operators, all can be detuned. So you can get amazing chorus like effects.
Like the "Epic pad" sound.
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Group 2 - Algorthms 7 to 18.

These are a mix of Tower & Branch (like a tree).

Of special note, Algorithms 16, 17 & 18 are pure frequency modulation. (there is no additive component). All FMs converge into operator 1.

 Use group 2 algorithms for things like Strings, Brass, Guitar, & Bass patches.
Examples: DX7 Voice ROM 1
A6 Strings (ALG 15)
A4 BRASS 3 (ALG 18)
A12 Guitar ( ALG 8)
A15 Bass 1 (ALG 16).

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Group 3 - Algorithms 19 to 25

These are rooting algos with or without a tower

There are at least 3 carriers in each of these algorithms.

Of particular note, Algos 23, 24 & 25 have one to 3 operators without any modulators.
These are pure sine wave carrier operators.
Group 3 algorithms are used for things like brass, Vibe & pipes.
For example see Voice ROM 1
A1 BRASS 1 (ALG 22),
A21 VIBE 1 (ALG 23)
A18 Pipes (ALG 19)

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Group 4 - Algorithms 26 to 32

These are tower/ branch combinations..
They all have at least 1 pure sine wave carrier only operator.

These are good for organ & bell sounds
Eg : from Voice ROM 1
A17 E.ORGAN 1 (ALG 32)

The Algorithm 32 is the simpliest algorithm.
Each operator is independent. Each generates a sine wave.
There is no Frequency modulation. Thus this is an example of pure additive synthesis.

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FM Index
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