Stereo Delay

Module ID fx.delay · Category Effect

A clap into the left side only, ping-ponged on worn tape: the first echo lights on the left, the second comes back on the right

The Stereo Delay plays back a copy of its input a moment later, then feeds that copy back in to make repeats. Filters in the feedback path darken or thin each repeat, P-P bounces the repeats between left and right, and Sync locks the time to the patch tempo.

Switch on Tape and it becomes a worn tape echo: the repeats waver in pitch, saturate as they build, and get darker each time around. Push the feedback far enough and they run away into the classic dub swell. The Tape module puts the same machine on a whole bus.

How it works

1. Each channel is written into its own delay line.
2. A read head plays the line back Time later. Reads usually fall between two samples, and a cubic (Catmull-Rom) interpolator fills the gap, so time changes and modulation glide smoothly instead of clicking or dulling the highs.
3. The playback runs through HiCut and LoCut, is scaled by FB, and goes back into the line with the input. Each repeat passes through the filters once more than the one before it.
4. Mix blends the dry input with the playback.

The display

The display draws the train of echoes. Time runs to the right from the moment a sound goes in. The first bar is the dry sound, and after it come the echoes, one delay time apart. Each echo is as loud as the feedback leaves it, on a decibel scale so a long tail stays readable. The left channel stands above the centre line and the right hangs below it.

• Filters. Every repeat passes HiCut and LoCut once more, so each bar is a little warmer than the one before and a little thinner. Tape mode adds the tape's own darkening.
• The sound going through. Each echo lights as the sound coming in reaches it, so a hit visibly walks down the train and fades. An echo lit to the top of its bar is as loud as the loudest thing that came in.
• Ping-Pong. With P-P on, the echoes take turns: each side's second echo is the other side's first, come back across. It shows best with something only on one side, or a stereo source.
• Tape. The bars blur and sway with the wow. Past unity, the feedback runs away and the header says so in orange.
• Words. The top left gives the time, with the note length when Sync sets it, in orange while Time CV moves it. The top right gives the feedback and the switches that are on.

Inputs

Outputs

Parameters

Time and FB keep working while their CV inputs are patched: the knob sets the center and the CV moves around it.

Feedback

In normal mode, feedback stops at 95%, and a soft clipper in the loop keeps the echoes from growing out of control. Around 30% gives a few echoes that fade naturally; 60% gives long trails; the top of the knob repeats almost forever.

In Tape mode the knob reaches further. See Runaway.

Tempo sync

Set Sync to a note length and the delay time follows the patch tempo. A Clock anywhere in the patch sets that tempo, so turning the Clock's BPM knob moves the echoes with it; they glide to the new time with a brief bend in pitch. With no Clock in the patch, the delay assumes 120 BPM. If a patch has more than one Clock, only one of them sets the tempo, so keep one Clock as the master.

Synced times can run past the Time knob's 2 seconds, up to 4.5 seconds: long enough for 1/4D at the Clock's slowest 20 BPM, so every division stays on the beat. Time CV still works while synced, swinging the synced time.

Tape mode

Tape models a tape echo: a loop of tape passing a record head and a play head. Switching it crossfades in about 15 ms, so you can flip it while echoes are still sounding.

Wow and flutter. The play head wanders. A slow wow (about 0.5 Hz, plus a slower drift of the reel) and a fast flutter (6 to 10 Hz) bend the pitch of the repeats by a few cents. The four motions run at unrelated rates, so the pattern doesn't loop.

Record-head saturation. The input and the feedback are recorded together through a soft, slightly lopsided curve. Quiet signals pass unchanged; loud ones round off and pick up the even harmonics of magnetized tape. Because the saturation sits inside the loop, a busy echo squashes and thickens as it builds.

Tape loss. Tape loses top end every time it records, so each repeat is darker than the last. Longer delays mean slower tape and darker repeats: the loss starts around 7 kHz at 250 ms and falls to about 3.5 kHz at one second. HiCut still works on top of it.

Motor glide. Time changes glide over about a quarter of a second, like a motor finding its new speed, and the repeats swoop in pitch as they go.

Runaway

In Tape mode, FB above about 90% pushes the loop past unity gain. The echoes grow until the record head's saturation holds them: the dub runaway. The output stays bounded at any setting, so you can ride it. Pull FB back below 90% and the echoes die away again.

Bypass

Click the power switch in the node header, press Ctrl+B with the module selected, or choose Bypass from its right-click menu. In L passes straight to Out L and In R to Out R (In R still copies In L when unpatched). The switch crossfades over 20 ms. A bypassed delay stops running, and it starts from silence when you switch it back in, so old echoes don't come back with it.

Patch ideas

Slapback. Time 80–120 ms, FB 0%, Mix 30%, Tape on. A single, slightly smeared echo, like a 1950s vocal.

Dotted-eighth rhythm. Sync 1/8D, FB 40%, Mix 40%. Turn on P-P with a stereo source and the repeats fall between the beats, alternating sides.

Dub throw. Sync 1/4 or 1/8D, FB 60%, LoCut 150 Hz, Tape on. For a bar, push FB up to the top and let it run away, then pull it back.

Chorus from a delay. A short time with the read head moving bends the copy's pitch:

[LFO Out] ──> [Delay Time CV]      Time 15–30 ms, FB 0–20%, Mix 50%

Ducking feedback. An inverted envelope pulls the feedback down on every hit, so the echoes swell back between them:

[Clock Gate] ──> [ADSR Gate]
[ADSR Out] ──> [Attenuverter In]   (negative Amount)
[Attenuverter Out] ──> [Delay Feedback CV]

Related modules

• Reverb: a diffuse space instead of distinct echoes
• Chorus: thickening without echoes
• Tape: the tape machine of Tape mode, for a whole bus
• Clock: sets the tempo Sync follows
• LFO: modulates the delay time