How Do I Measure Stereo Phase on an Oscilloscope?
To compare stereo phase in BeamTracer OSC-1, enable SCOPE in the bottom VISUALIZERS strip, then press MEAS above its waveforms. OSC-1 shows the left and right traces on a shared trigger and reports R lags L in degrees. Test the readout with the Oscillator's CIRCLE, LINE and ELLIPSE presets.
Hi, I'm Trina with BeamTracer.com. The XY picture gives you a shape, while the two waveforms show where each channel is in its cycle. Watching both makes it easier to understand why a circle becomes an ellipse or a diagonal line.
Watch me read the phase on a circle, a line and an ellipse, flip the right channel to 180°, overlay both waveforms and send the signal to the laser simulator:
One live 200 Hz sine source: CIRCLE, LINE, ELLIPSE, then CIRCLE. Watch the XY figure and R lags L together. This walkthrough is silent.
How do I display the phase measurement in OSC-1?
Turn on SCOPE in the bottom VISUALIZERS strip, keep the strip in ANALYSIS, and press MEAS in a SCOPE panel header. The panels show LEFT and RIGHT waveforms, their frequency and levels, and the relative phase readout. SCOPE is a second view of the source; the large XY drawing remains above it.
- Open OSC-1 and select CREATOR.
- Expand GENERATORS, then OSCILLATOR.
- Set FREQUENCY → 200 Hz, select SINE, and choose CIRCLE with both X and Y channels enabled.
- Select SCOPE in the bottom VISUALIZERS strip and keep ANALYSIS enabled.
- Press MEAS above a waveform and read R lags L alongside the two traces.
- Choose LINE or ELLIPSE in the Oscillator card and compare the changed readout and XY picture.
- Open EXPORT → VIDEO, select your frame size and resolution, and use RECORD LIVE INPUT followed by STOP RECORDING to save the XY picture and source sound as WebM.
If the keyboard takes up space, press HIDE KEYS before comparing the pictures. The input keeps running. The recording step saves the XY artwork; it does not record the surrounding SCOPE measurement panels. The examples in this article are interface walkthroughs so you can see those controls.
Keep the input simple
Use the same SINE source and 200 Hz frequency for all three presets. Changing only phase makes the relationship easier to see. A full song contains many frequencies and does not behave like this single-tone experiment.
What do the circle, ellipse and line tell me?
With equal-amplitude sine waves at the same frequency, LINE puts both channels at the same phase, ELLIPSE sets a 45° difference, and CIRCLE sets a 90° difference. OSC-1 maps the left channel to X and the right channel to Y, so that relative timing changes the XY shape.
| Oscillator preset | Phase readout in this example | XY picture |
|---|---|---|
| LINE | R lags L 0.0° | Rising diagonal |
| ELLIPSE | R lags L 45.0° | Tilted ellipse |
| CIRCLE | R lags L 90.0° | Circle |
At 200 Hz, a cycle takes 5 milliseconds. A quarter-cycle shift is 90°, or 1.25 milliseconds. Keep that relationship in mind while comparing the peaks in the left and right traces. SCOPE starts both panels at the same instant, so their offset remains visible even though the waveforms are held steady by triggering.
Unequal channel levels can turn the circle into an ellipse too. A shape alone does not uniquely identify a phase difference unless you also know the source and channel amplitudes. The Lissajous guide explains the separate effect of changing the X/Y frequency ratio.
What happens at 180°?
Set the Oscillator's X (Left) phase to 0° and Y (Right) to 180° for equal and opposite sine waves. The XY picture becomes a falling diagonal. Return Y to 0° for the rising diagonal, then 90° for the circle.
The frequency stays at 200 Hz while the right-channel phase changes. The 180° state puts peaks in one channel opposite troughs in the other.
A phase angle repeats every full cycle. OSC-1 reports the right channel's lag from 0° up to 360°; a full-cycle shift returns to the same phase. Use the waveform traces to check which part of the cycle each channel occupies.
This measurement is easiest to interpret with a steady periodic signal. A fluctuating number on complex music is not a single permanent delay for the entire mix. It also does not tell you whether every frequency will combine well when summed to mono.
How do I put the waveforms on top of each other?
Open Settings → VISUALIZERS → XY SCOPE and choose Layout → OVERLAY to put both channel traces in one panel. STACKED gives each channel its own panel. Use Time to change the displayed window; you can also scroll over the SCOPE panels to zoom it.
The default cyan and coral traces help distinguish left from right. Keep both channel gains and offsets consistent when comparing their shapes. AUTO sizes and centers the traces for viewing, so the drawn height is not a direct voltage measurement.
Read the units
MEAS reports digital frequency and levels, including peak and RMS in dBFS. Those are measurements of the digital signal in OSC-1, not microphone sound pressure or calibrated electrical voltage. A missing phase value needs a suitable signal in both channels.
How do I save the experiment as a video with sound?
Use EXPORT → VIDEO → RECORD LIVE INPUT to record the current XY display and audio graph together. Change the phase during the take, then use STOP RECORDING to download the WebM. Check the downloaded video before putting it in an editor.
Silent interface walkthrough of the recording route. The downloaded recording contains the XY picture and the generated tone; the waveform panels and interface are outside that output.
For a full recording walkthrough, see record oscilloscope art with sound. For a diagonal picture that you did not intend to create, start with why mono audio draws a line.
Compare the circle, ellipse and line on the same source.