Alluvial
A tape loop that wears · Radish · Vulpus Labs
Alluvial is a stereo tape loop for drones. It holds up to a minute of sound, with erase, record and playback heads. Each pass changes the sound a little.
Tape feedback is an old way of making drones: record a sound, play it back, and record the playback over itself. Each new layer mixes with what's already there. As the tape wears, the sound gets darker, softer and quieter, with a little noise. Eventually it settles into the background or fades beneath newer layers.
Alluvial models this as tape wear, not as an effect applied to the output. The changes are written back to the tape, so they build up with each pass. The record head loses high frequencies first. The erase head removes high frequencies faster than low ones. Noise recorded onto the tape wears down along with everything else, leaving a dark wash rather than an ever-growing hiss.
You can also damage the tape. Thin patches in the oxide make the sound drop out in the same places on each pass. These patches can gradually spread.
Wear is measured in passes, not seconds. A short loop therefore wears faster than a long one, just as real tape does.
To begin: patch a drone into IN L, then connect OUT L and OUT R to your output. MIX starts on TAPE, so you hear the tape rather than the direct input. The tape starts blank, with only a faint hiss.
Press REC. The red line in the display marks the record head. Your drone is recorded as the tape passes it, and you hear it when it reaches the play head. After a pass or two, press REC again to stop recording. The loop keeps playing and slowly wearing for as long as you leave it running.
The machine
The controls on the left operate the tape machine itself.
IN L and IN R are the audio inputs. A signal of ±5 V fills the tape's recording range. If IN R is unpatched, IN L feeds both tracks.
REC starts and stops recording. The red button is a toggle and lights up while recording. The REC jack does the same while its voltage is above 0 V. Recording continues while either the button or the jack is active.
Starting or stopping a recording crossfades over a few milliseconds to avoid clicks. When REC is off, the record and erase heads stop working, but the tape keeps playing.
CLEAR erases the whole tape. It fades the sound out over a quarter of a second rather than cutting it off, then returns the tape to blank, with its original damage restored (see Damage below). The button operates manually; the CLEAR jack triggers a wipe each time its voltage rises above 0 V.
STOP brakes the tape motor. The tape slows down, its pitch falls, and its sound fades as it comes to a halt. Turn STOP off and the tape speeds up again. The button is a toggle; the STOP jack holds the tape stopped while its voltage is above 0 V. The tape stops if either control is active. Hover over the button to see what it is doing.
OUT L and OUT R, in the red-orange section, are the two output tracks. MIX controls the balance between the tape and the input. The right track's heads sit a fraction of a millisecond behind the left track's, like slightly misaligned tape heads. This gives the stereo image a little extra width.
SPLICE sends a 1 ms, +5 V trigger each time the splice passes the heads, in either direction. This happens once per loop. Patch it into Glacial's RESET to restart the drum in time with the tape loop.
The tape itself is not saved with the patch. Loading a patch gives you blank tape, but the knobs and switches are saved as usual.
The display
The display across the top shows the whole loop moving from right to left past the fixed heads.
- The red line, REC, marks the record head. A small tick just before it marks the erase head.
- The black line, PLAY, marks the playback head. GAP sets how far behind the record head it sits.
- The dashed line marks the splice, which moves with the tape.
The waveform shows the level the play head would hear at each point on the tape. The pale trace shows the peak level; the darker area shows the average.
The display uses a decibel scale extending 48 dB below full level. This lets you see sounds fading over hundreds of passes: as a section wears away, its trace becomes paler.
Damaged sections of tape are shaded red.
TAPE
LENGTH sets the loop length, from 1 second at the left end of the control to 60 seconds at the right. The range is spread evenly by ratio, rather than by seconds. The default is about 21.6 seconds.
Changing LENGTH does not move the heads or splice the tape immediately. The new length takes effect when the tape next reaches the splice, so turning the knob does not cause a click. The setting at that moment is the one that counts.
If you shorten the loop, the material beyond the new end remains on the tape. It simply won't play until you lengthen the loop again.
Hover over LENGTH to see the current duration, for example:
Length: 21.6 s
TAP sets the loop length from an incoming clock. The time between two rising edges above 0 V becomes the loop length, from 1 to 60 seconds. The new length takes effect at the next splice, just like a change to LENGTH.
Until TAP receives two rising edges, and whenever it is unpatched, LENGTH's knob sets the loop length. The tooltip shows both values, for example:
Length: 8.00 s from TAP (the knob: 21.6 s)
SPEED controls tape speed, from half speed at the left end, through normal speed (1x) in the centre, to double speed at the right. It starts at 1x.
Speed affects both recording and playback. Record something at half speed and play it back at 1x, and it sounds an octave higher. Recording layers at different speeds lets them sit at different pitches.
Slower tape also loses more high frequencies. At 1x, the tape holds frequencies up to about 16 kHz; at half speed, that limit drops by an octave.
Hover over SPEED to see the current ratio, for example:
Speed: x1.000
GLIDE controls how quickly the tape responds to a change in SPEED, like the inertia of a capstan. At the left end, the response takes 5 ms and is almost instant. At the right, it takes 5 seconds. It starts at about 40 ms.
When the speed changes, the pitch glides rather than jumping immediately. Hover over GLIDE to see the current time.
CV and AMT beside SPEED let a control voltage change the tape speed. AMT sets the depth, with no modulation at the centre. At maximum AMT, ±5 V changes the pitch by half a semitone in either direction. A quarter of the way from the centre gives about ±3 cents. Turning AMT left of centre reverses the modulation.
This input is intended for vibrato and chorus, not large pitch changes. Hover over AMT to see the depth, for example:
Speed CV: +12.5 cents at 5 V
WOW and FLUTTER add the small speed changes of a real tape machine.
WOW is the slower movement, between half a cycle and two cycles per second. Its rate and depth drift slightly from one cycle to the next, like an uneven reel.
FLUTTER is faster, between 6 and 16 cycles per second, with a little extra roughness.
WOW can reach ±3% of the tape speed; FLUTTER can reach ±1%. The first half of each control covers the range of a good tape machine. Both start at subtle settings: ±0.12% for WOW and ±0.023% for FLUTTER. They affect both tracks.
Hover over either control to see its depth.
SNAG sets how much damaged tape drags against the heads. When a damaged section passes, the tape briefly slows and the pitch drops.
At the left end, damage only reduces the sound level. At the default setting, bare tape slows the tape by 8%, about one and a half semitones. At the right end, the slowdown reaches 16%.
Hover over SNAG for the current amount, for example:
Snag: bare tape drags 8.0%, -1.44 semitones
REV and FWD set the tape's direction. Reversing direction takes time: the tape brakes, stops and accelerates the other way. The pitch falls to nothing and rises again as it does so.
At 1x, changing direction takes about half a second. A longer GLIDE setting makes it take longer.
The TRIG jack beneath the direction switch reverses the tape each time its voltage rises above 0 V. The switch determines which direction the tape runs between triggers.
HEADS
INPUT sets the recording level. At the left end, nothing is recorded. In the centre, the input is recorded at its original level. At the right end, the level is multiplied by four (+12 dB).
The default is +5.8 dB. Hover over INPUT to see the current gain.
ERASE controls how much the erase head removes on each pass while recording.
High frequencies are easier to erase than low frequencies, because the low frequencies sit deeper in the tape's coating. As a result, erasing makes the sound darker as well as quieter.
At the left end, nothing is erased. When recording over a loop, every layer remains, subject to the other forms of wear. The bottom of the control is very fine-grained, changing the level by fractions of a decibel per pass.
At the right end, the tape is completely erased on each pass, giving you a conventional tape delay.
Hover over ERASE to see the loss per pass at 1 kHz, and how long it would take a sound to fall by 60 dB at the current loop length and speed. For example:
Erase: -0.9 dB a pass, 60 dB in 4:20
CV and AMT beside ERASE let a control voltage change the erase amount. AMT sets the depth, with no modulation at the centre. At maximum AMT, ±5 V sweeps ERASE across its full range.
GAP sets the distance between the record and playback heads as a proportion of the loop. At the left end, the heads are together. At the right end, the play head is a full loop behind the record head. The default is halfway.
Because GAP is a proportion of the loop rather than a fixed time, the echoes produced by FEEDBACK stay at the same points in the loop when you change LENGTH. A quarter-loop gap always gives four evenly spaced echoes per loop.
Moving GAP moves the playback head, and the pitch bends as it would when moving a real tape head.
Hover over GAP to see the proportion and its equivalent time, for example:
Gap: 50% of the loop, 10.78 s
FEEDBACK sends the playback signal back to the record head while recording. The new signal replaces an equivalent amount of what was already on the tape, so the loop never gets louder without limit. FEEDBACK starts off.
With ERASE fully right, the result is a conventional tape echo. Echoes are spaced according to GAP, and each is quieter according to the feedback setting.
At maximum FEEDBACK, the playback signal replaces the loop, leaving a loop whose length is set by GAP. Hover over FEEDBACK to see the current amount.
MIX sets the balance between the direct input (DRY) and the tape (TAPE) at OUT L and OUT R. It starts on TAPE, so you hear the loop rather than the direct input.
WEAR
The controls in this row set the losses and noise added by the tape. They act on each recording pass. With REC off, playback still wears the tape, but at one tenth of the normal rate.
HIGHS sets how much high-frequency content the record head loses on each pass. The loss is a shelf starting above about 3 kHz. It builds up over time, gradually lowering the frequency range the tape can reproduce.
There is also a very small loss across the whole frequency range. This lets a loop fade away even if ERASE is set to zero.
At the default setting, each pass removes 0.6 dB from the top end.
Hover over HIGHS to see the loss per pass, for example:
Highs: -0.60 dB a pass
SAT models tape saturation. Below a certain level, the tape records the signal accurately. Above that level, the signal bends gently towards a ceiling.
Turning SAT up lowers the level at which saturation starts, from 5 V, and brings the ceiling down sharply. At the default setting, saturation starts at 4.7 V and the maximum level is 7.6 V.
Hover over SAT to see the current values, for example:
Sat: from 4.7 V, at most 7.6 V
HISS controls two kinds of tape noise.
Playback hiss comes from the tape's own surface. You hear it even on blank tape, and it is not recorded back onto the tape.
Recording noise is added each time you record. It then wears down like the rest of the signal. Eventually, the amount being added on each pass balances the amount being lost, leaving a dark wash beneath the sound rather than an ever-louder hiss.
The default playback hiss is 60 dB below 1 V.
Hover over HISS to see its level, for example:
Hiss: -60 dBV
GRAIN adds noise caused by small variations in the tape surface. A recorded tone carries a faint, moving fuzz.
You hear this noise during playback, and each recording pass adds more at half the depth. It therefore builds up over successive generations.
Hover over GRAIN to see its level relative to the signal, for example:
Grain: -41 dB of noise on the signal
PRINT models print-through. On a real reel, layers of tape lie against one another and faintly copy their sound onto neighbouring layers.
Here, each recording pass adds a faint echo of the material about one second away on either side. The copy is louder after the original than before it. The first half of the control gives the faint ghosting heard on real tape.
Hover over PRINT to see the amount added per pass, for example:
Print: -62 dB a pass
WEAR, from NEW to OLD, scales HIGHS, SAT, HISS, GRAIN, PRINT and the tape damage controls together.
At NEW, the tape is perfect regardless of the other settings: there is no signal loss or recorded noise, and only half the playback hiss remains.
At the centre, where the control starts, each effect is at the level set by its own control.
At OLD, each effect is four times as strong.
Hover over WEAR to see the current setting, for example:
Wear: 50%, the losses x1.00
Damage
DROPOUT sets how much damage the tape starts with. The tape has scattered patches, 5–50 ms long, where the oxide is thin. When these patches pass the play head, the sound becomes quieter and duller.
The patches are fixed in place on the tape, so they occur at the same points on every pass. They become part of the loop's rhythm.
At low settings, there are only a few faint dropouts. Turning the control up adds more and makes them deeper. At the default setting, there are about five spots per minute of tape.
Hover over DROPOUT to see the number, for example:
Dropout: 4.8 spots a minute of tape
DISINTEGRATE sets how quickly the damage gets worse. Each time a damaged patch passes the heads, it deepens slightly and spreads into neighbouring areas. The holes widen over time, and new small spots occasionally appear.
At maximum DISINTEGRATE, with WEAR at its default setting, a loop can fall apart in a few dozen passes. At low settings, this takes hundreds of passes.
DISINTEGRATE starts off. Damage grows whether or not REC is on, and once it has developed, it stays until you clear the tape. Hover over the control to see its rate.
Sound lost through a damaged patch is lost once. Recording over that patch later loses the same part of the signal, but the patch does not keep removing more sound simply because it has been there longer.
CLEAR restores the tape's original pattern of damage, removing any damage that has developed.
Jacks
| Jack | Direction | Function |
|---|---|---|
| IN L | In | Left track input; ±5 V fills the tape's recording range |
| IN R | In | Right track input; IN L feeds both tracks if this is unpatched |
| REC | In | Records while the voltage is above 0 V |
| CLEAR | In | Fades and erases the tape on each rising edge above 0 V |
| STOP | In | Stops the tape while the voltage is above 0 V |
| TAP | In | Sets loop length from the time between two rising edges above 0 V |
| CV (SPEED) | In | Modulates speed; at maximum AMT, ±5 V gives ±50 cents |
| CV (ERASE) | In | Modulates ERASE across its full range at maximum AMT and ±5 V |
| TRIG | In | Reverses tape direction on each rising edge above 0 V |
| OUT L | Out | Left track, mixed with the input according to MIX |
| OUT R | Out | Right track, mixed with the input according to MIX |
| SPLICE | Out | +5 V trigger lasting 1 ms each time the splice passes the heads |
All input jacks read 0 V when nothing is connected.
Notes
The loop cannot run away. FEEDBACK replaces existing material rather than adding to it indefinitely. The erase head and record-head bias never increase the signal at any frequency, and SAT limits the maximum level. Even an hour of recording over a loop with no erase leaves the signal at a bounded level.
Recording over a loop with ERASE at zero still wears it. The record-head bias is responsible for most of the darkening in sound-on-sound recording. HIGHS controls how much.
Short loops wear faster. Each loss happens per pass. A two-second loop makes 30 passes a minute; a 60-second loop makes one.
Stopping and reversing are audible. The tape slows and speeds up like a real motor-driven tape machine. Its sound falls away as it approaches a stop.
Starting points
An hour of wear
Patch a Littoral drone into IN L and set LENGTH to about 20 seconds. Record two passes, then stop recording. Leave the tape playing with WEAR at its centre and DISINTEGRATE turned up a little. Over the next hour, the loop darkens, the damaged patches widen, and the drone gradually sinks into the tape.
Sound-on-sound
Leave REC on, turn FEEDBACK off, and set ERASE low. Feed a changing drone into IN L. Each pass adds the new sound over the old, while ERASE and HIGHS gradually remove the earlier layers. ERASE's tooltip tells you how long a layer takes to fade by 60 dB.
A composed erase
Patch a Glacial lane into ERASE's CV input. Set AMT fully right, ERASE to zero, and turn REC on. Draw the lane high where you want the loop erased, and low where you want the sound to build up.
Two speeds, an octave apart
Record a drone at 1x. Turn SPEED fully left to half speed and record another layer over it with ERASE low. The first layer now plays an octave lower, while the new layer plays at its original pitch. Turn SPEED back to 1x: the first layer returns to its original pitch, and the second plays an octave higher.
A tape echo
Set MIX halfway, turn REC on, set ERASE fully right, put GAP at one quarter, and set FEEDBACK to about halfway. You get four echoes per loop, each quieter and darker than the last.
A score in time with the loop
Patch SPLICE into Glacial's RESET. Each time the tape completes a loop, the drum resets to the splice. A lane drawn on the drum will therefore fall in the same place in the loop on every pass.
A spiral
Patch a drone and OUT L, mixed together, into Calderal's A IN 1. Set Calderal's SIDE to SUM and SHIFT on WIDE to a few hertz. Patch its OUT 1 into Alluvial's IN L.
Turn REC on, set ERASE fully right, and turn FEEDBACK off. Each time the sound passes around the tape, it returns shifted a little further.
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Radish Alluvial
$10.00