⚡ ImpedanceScope — Setup & Use Guide

For the audio interface version described in the blog post.
→ Open the tool

What you need

A stereo USB audio interface with at least one output and two inputs (left & right). See interface notes below.
A series resistor Rs — a known precision resistor, typically 1 kΩ. This is your reference component.
Two short cables or probes to connect CH1 and CH2 inputs to your circuit.
Chrome or Edge browser (required — Firefox cannot select output devices).

How to wire it up

Connect everything in series like this:

GND ── DUT(Z) ── Left input (CH1) ── Rs ── Right input (CH2) ── Audio output

Audio output (headphone/line out) feeds the sine wave stimulus.
Left input (CH1) measures the voltage across the DUT.
Right input (CH2) measures the voltage after the series resistor Rs.
All grounds are connected together at one point.

Set Rs in the sidebar to match the actual resistor value you have wired in.

First time setup

1Disable Windows audio enhancements

This is the most important step. Windows applies noise cancellation and loudness equalisation to audio devices by default. These corrupt the measurements entirely.

For each device (both playback and recording):
Sound Settings → device → "Device properties" → "Additional device properties" → Enhancements tab → check "Disable all enhancements".

Or run disable_audio_enhancements.bat as administrator (from the same folder as this guide) to do it automatically for all devices at once. You may need to repeat this after unplugging and re-plugging the interface.

2Set the input to Stereo (2-channel)

In Windows Sound settings, find your audio interface under Recording devices. Open its properties and make sure the format is set to 2 channel (stereo), not mono.

If the tool shows ⚠ Input is MONO in the console after starting, this is what needs fixing.

3Open the tool and grant microphone access

Open the tool in Chrome or Edge. A prompt appears asking for microphone permission — click Allow. This is required for the browser to access audio input.

After clicking Enable Audio on the splash screen, the device dropdowns will populate with the names of your audio interfaces.

4Select your input and output devices

Under Audio Interface in the sidebar:

Set Input device to your audio interface's input (not "Default" — pick it by name).
Set Output device to the same interface's output.
If your device does not appear, click ↺ Refresh devices.

Using the same physical interface for both input and output ensures the stimulus and measurement share the same clock and ground.

Running a measurement

Wire up your DUT and Rs as shown above.
Set Rs (Ω) to match your series resistor.
Set f₀ and f₁ — the start and stop frequency. Default 20 Hz – 20 kHz covers the full audio range.
Click ▶ Start. The tool plays a sine wave through the output and measures both channels as it steps through frequencies.
Results appear live in both the Bode plot (magnitude and phase vs. frequency) and the Smith chart.
When done, click ↓ Save CSV to export the data.

You can run multiple sweeps — each one is added to the Sweeps list in a different colour. Click a sweep label to make it active (bold on the charts).

Audio interface notes

Interface	Works out of the box?	Notes
MOTU M4	Yes	Professional, simultaneous stereo sampling, no calibration needed
Cubilux CA7	Yes	Budget USB-C, 24-bit, performs on par with the M4
Behringer UCA222	With calibration	16-bit TDM ADC — Ch2 leads Ch1 by exactly 1 sample. Set Ch2 timing correction = −1. Also has ~8.5 kΩ input loading. Use Open+Load calibration.
Built-in sound card	Maybe	Typically works for rough measurements. Shared ground with PC may introduce noise. No dedicated line output.

Budget interfaces: many cheap interfaces have inter-channel timing skew (one sample delay between L and R), low input impedance, or roll-off at the frequency extremes. Use the Calibration procedure below to compensate.

Calibration (recommended for budget interfaces)

Calibration corrects for input loading, inter-channel phase errors, and cable parasitics. Two measurements are taken with known conditions:

1Open calibration — DUT disconnected

Remove the DUT, leaving the CH1 probe dangling open (nothing connected to it). Click ↺ Open cal. The tool does a full sweep and stores the result.

2Load calibration — known resistor as DUT

Connect a known, accurate resistor as the DUT (e.g. 1 kΩ). Enter its value in Load resistance (Ω). Click ↺ Load cal. The tool sweeps again and stores this reference.

3Enable calibration

Tick Apply calibration. Now reconnect your actual DUT and run a sweep. All subsequent measurements will be corrected.

To discard calibration data click ✕ Clear.

Tips

Rs value matters. For best accuracy Rs should be in the same order of magnitude as the DUT impedance. For a 100 Ω DUT use 100 Ω, for a 10 kΩ DUT use 10 kΩ.
Amplitude. Start at 0.5. If the console shows very low dB on CH1 or CH2, increase it. Avoid clipping (some interfaces clip at full scale).
Ch2 timing correction. If phase looks wrong by a constant offset that gets worse at high frequencies, your interface has ADC skew. Try −1 for the UCA222. Other interfaces: 0.
Smith chart Z₀. Set this to match Rs for the most useful view. It updates automatically when you change Rs.
Hover the Smith chart to read out frequency, |Z|, and the equivalent L or C at each point.
Load reference lets you overlay a previously saved CSV for comparison.