A-Oscilloscope

Fwuzeem Audio A-Series

What it is

A-Oscilloscope is a real-time waveform visualizer with a vector-style scope display, selectable time window, and rolling or triggered updates. It captures incoming samples in a circular buffer and draws a waveform from the recent capture. The audio path is bit-perfect pass-through: no waveform scaling, trigger operation, or other display setting changes the samples sent to the output. V-Shift is a display-only plot zoom.

Controls & parameters

Parameter ID	Display name	Range	Default	What it does
`gain`	V-Shift	-20.0 to +20.0, step 1.0	0.0	Applies a visual plot multiplier of `2^shift`, or about +/-6.0206 dB per step, before the display auto-fit. It does not change audio.
`window`	Window	5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 150 ms, 200 ms	10 ms	Sets the displayed timebase window.
`trigger`	Trigger	Rolling, Free, Rising, Falling	Rolling	Selects continuous scrolling, an unsynchronised recent window, or a zero-crossing trigger direction.

The V-Shift knob uses the house rotary range of pi*0.82 to pi*2.18 with a stop at the ends. The display trace is fitted to its observed peak after the multiplier is applied, so the multiplier cancels in the normal rendering path and does not provide a persistent visible zoom. It never acts as an audio gain stage.

Trigger modes work as follows:

Rolling continuously shifts the display as new samples arrive.
Free displays the most recent window without zero-crossing alignment.
Rising searches for a negative-to-non-negative zero crossing and rotates the display to that point when one is found.
Falling searches for a positive-to-non-positive zero crossing and rotates the display to that point when one is found.

The trace is built from the average of the left and right captured samples. The screen includes a center reference line for zero amplitude.

Workflow / how to use it

Insert A-Oscilloscope at the point where the waveform needs to be inspected.
Start with Rolling and a 10 ms window to see the signal’s general shape.
Shorten the window to 5 ms or 10 ms for transients and individual cycles. Lengthen it to 100 ms, 150 ms, or 200 ms for slower or rhythmic material.
Choose Rising or Falling when a repeating waveform needs a stable zero-crossing reference. Use Free when alignment is not wanted.
Leave V-Shift at 0 unless you need to preserve a saved display state. The current auto-fit cancels its apparent plot scaling, and the pass-through audio is unchanged at every setting.

Use cases

Polarity and phase sanity checks. Watch the summed trace while checking a polarity reversal, a duplicated path, or a time-alignment change. Cancellation or a reversed-looking waveform is a useful warning, but this single trace is not a substitute for separate left/right analysis.
Transient inspection. Select a short window such as 5 ms and inspect the shape and timing of a drum hit, pluck, edit, or leading edge without inserting an audio-processing stage.
Triggering rhythmic content. Use Rising or Falling to align repeating cycles or pulse-like material to a chosen zero-crossing direction. Use Rolling to watch the waveform move continuously.

Specs & requirements

Formats: AU and VST3.
Audio layouts: matching mono or stereo input and output layouts; the normal configuration is stereo.
Processing: FP32 and FP64 audio processing are supported.
Audio latency: no intentional audio delay; capture and drawing are outside the audio path. Tail length is 0 seconds.
MIDI: no MIDI input or output; this is not a MIDI effect.
Programs and state: one host program; parameter state is stored as APVTS XML.
Platform target: macOS 10.15 or later.
Build: use the shared CMake pipeline from the A-Oscilloscope folder (cmake -B build, then cmake --build build).

Notes / caveats

A-Oscilloscope performs no audio DSP. Its output is the input passed through unchanged, apart from normal host bus-layout handling.
The audio thread writes captured samples to a fixed 32,768-sample ring buffer. The waveform display reads that buffer on the GUI timer and clamps its window to 32 through 16,384 samples; at high sample rates, a requested 200 ms window can therefore be shorter than its label. This does not add audio delay.
Rising and Falling are zero-crossing searches, not threshold, hysteresis, or derivative triggers. If no matching crossing is found in the search region, the recent window remains available without a new alignment.
The visual trace averages the captured left and right channels. It should not be read as two independent channel traces.
V-Shift multiplies the captured display samples, but the current peak auto-fit cancels that multiplier during normal rendering. It cannot increase headroom, fix clipping, or change polarity in the audio path.