DOPPLER
A moving-source effect for the Critter & Guitari Organelle
User Manual – Version 1.8
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1 WHAT IT IS
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Doppler makes whatever you feed it sound like it is moving around
you. Not a panner with a filter on it: the patch keeps a position in
metres, works out how far that position is from each of your ears,
and derives everything from that one number.
Two engines run, one per input channel, each with its own settings.
Or one, if you leave it in mono – which is how it starts.
AT A GLANCE
* Engines – 2, one per input channel, independently configurable
* Controls – 4 knobs, two pages (one per channel)
* Keyboard – two global settings: Bend and orbit
* Modes – glide or jump, set by knob 2
* Audio in – stereo or mono; a mono source is detected and copied
* MIDI – not used
* Best on headphones – see below
HEADPHONES
This is more of a studio effect than a guitar pedal, and it wants
headphones, or a pair of well positioned speakers.
The position of the source is carried partly by the tiny
difference in arrival time between your two ears – the patch renders
each ear separately rather than panning – and that cue survives
headphones intact while a pair of speakers in a room largely washes
it out. On monitors you still get the pitch bend, the level swell
and the reverb, which is plenty; on headphones the thing actually
moves around your head.
COMPATIBILITY
Developed and tested on an Organelle M running Organelle OS 4.1.
Plain Pure Data vanilla – no externals, no extra libraries.
Original Organelle (Organelle 1): untested. It should load, but the
geometry is computed with expr~ objects at audio rate and the older
single-core machine may find two engines plus reverb a lot. Please
report back if you try it.
ORAC: not at the moment. Same reasoning as the other patches – an
ORAC module has different host conventions and parameter pages
instead of four fixed knobs, so it would be a real port.
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2 GETTING SOUND INTO IT
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Plug an instrument into the Organelle input. Stereo in gives you two
independent moving objects, one per channel.
If you only have a mono source in one socket, the patch notices the
silent side and feeds it the live one, so both engines still have
something to move. It is quick to spot a channel appearing and slow
to declare one dead – one and a half seconds of near silence – so a
pause in your playing will not make the routing flip mid-phrase.
The effect is entirely wet-and-dry balanced by knob 2: at zero the
patch passes the signal through untouched.
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3 THE CONTROLS
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Four knobs, two pages. Push the rotary encoder to switch pages; the
fifth screen line tells you which page you are on. Knobs act
immediately, so the first move after a page switch jumps that page’s
value to where the knob physically sits.
KNOB 1 – DISTANCE
How big the loop is, from about a metre and a half across to about
forty. Where the loop sits relative to you is set on the keyboard –
see section 5 – so Distance changes the size of the movement, not
how far away it is.
It also sets how much high end is lost at the far end, how much
reverb is sent, and how long the reverb tail is. Far away means
darker, wetter and longer.
KNOB 2 – MOVEMENT SHAPE
The sign is the direction of travel, so -40 and +40 are the same
path walked in opposite directions. Setting the two pages to
opposite signs puts the two objects on opposite sides of the loop,
which is what makes stereo sound like two things rather than one
wide thing.
The knob is a mirror about its midpoint. Both ends are calm and the
two halves meet at their wildest.
* 0 – off. The channel passes through dry.
* 1 to 50 – glide. Screen reads “Shape glide”.
* 51 to 100 – jump. Screen reads “Shape jump”.
GLIDE, 1 TO 50
A clean circle at the bottom. As you turn it up the circle keeps its
overall roundness but its radius starts to wobble, so the path grows
lobes and dents – by 50 it is something like a lumpy heart rather
than a circle. The closest approach stays exactly where the orbit
setting puts it at every Shape value, so the character of the pass
does not change as you turn this knob; only the route between passes
does.
JUMP, 51 TO 100
The path is cut into slices, and each slice is moved and resized on
its own. Picture a drawn circle cut into thirty pieces with the
pieces nudged about: still recognisably a circle, but a broken one.
The source glides along each slice at its normal speed, so every
slice has its own approach, retreat and doppler – it is not a series
of static positions.
51 is the wild end: slices thrown far from where they belong, so the
figure barely holds together. Towards 100 the displacements get
smaller and rarer and the underlying shape settles into a circle, so
100 is a gently broken ring.
KNOB 3 – MOVEMENT SPEED
How fast the source travels, from a slow walk to about 30 metres per
second – roughly a car going past. The lap time follows from that
and from how big the loop is, so a large loop at the same speed
takes proportionally longer to come round. At zero the source parks
where it is, which is a way to freeze it at one position.
KNOB 4 – SPACE / REVERB
Reverb amount, scaled by how far away the source currently is. The
send breathes with the movement rather than sitting at a fixed
level, and the tail is fed after the doppler so it is not
pitch-smeared.
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4 MONO AND STEREO
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Press Aux to switch. The LED shows which you are in: yellow for
mono, red for stereo. The patch starts in mono (the output is stereo
of course), with one page and one moving object.
Whichever page you are on when you press Aux becomes the master: its
four values are copied to the other channel at once, and every later
change mirrors in that direction. Switching back to stereo leaves
both channels holding those values, so nothing is lost.
In mono only one engine runs and both inputs are folded into it.
This matters: two engines with identical settings are not the same
thing as one, because they drift apart by however many milliseconds
separate their starts, and that sounds like a short delay rather
than one object.
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5 THE KEYBOARD – BEND AND ORBIT
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The keyboard sets two global things. They apply to both channels,
and both are shown on screen line 5, which reads something like
CH-L Bend 2 PASS
LOWER HALF – BEND 1 TO 4
How far the pitch bends. The bend depends on the ratio between two
speeds: how fast the source moves, and how fast sound moves. There
are two ways to make that ratio bigger. Move the source faster –
that is knob 3, and it works the way you would expect. Or make sound
slower – that is Bend.
Sound really travels at 343 metres per second, so a source doing 30
is moving at about a ninth of that and bends the pitch modestly. If
sound crawled along at a quarter of its real speed, the same source
at the same 30 metres per second would be much closer to outrunning
its own wavefronts, and the pitch would bend four times as far.
* Bend 1 – a quarter of the real bend. Movement you hear mostly as
level and position.
* Bend 2 – the real world. About a semitone and a half at full
Movement Speed. The default.
* Bend 3 – double.
* Bend 4 – quadruple, roughly six semitones. Well past plausible,
which is sometimes the point.
Bend only affects pitch. Level, panning and reverb are unchanged
by it.
UPPER HALF – ORBIT
Where you are standing relative to the loop. Distance sets how big
the loop is; this sets whether you are on its rim or in the middle
of it, and that is what decides the character.
* PASS – you are on the rim. It comes within a third of a metre and
flies past your head, loudest at that moment. The default.
* NEAR – just outside the rim. Passes close by rather than through
you.
* WIDE – you are inside a wide loop. At Distance 45 the source runs
between about four and sixteen metres away.
* RING – nearly concentric. At Distance 45 it stays between eight
and eleven metres and simply circles you.
RING is deliberately not perfectly centred. A path at a constant
distance would have no doppler and no swell at all, only panning, so
a little eccentricity is left in to keep both.
The four are level-matched to within about a decibel of each other,
so you can compare them without reaching for the volume.
