ac — audio measurement CLI

Command-line toolkit for audio bench measurements.

THD, THD+N, level 'n frequency sweeps, transfer functions, live spectrum.

The ip of audio — terse, positional, unit-tagged arguments.

Alpha — only tested on Linux with JACK (native and PipeWire). sounddevice/PortAudio backend exists but is not exercised yet. macOS and Windows are untested.

Install

pip install -e .

This gives you the ac command.

Audio backend

ac auto-detects the audio backend at startup:

Backend	When used	Platforms
JACK (jack-client)	Preferred when a JACK server is running	Linux (native or PipeWire)
sounddevice (PortAudio)	Fallback when JACK is unavailable	Linux, macOS, Windows

To force a backend, set "backend" in ~/.config/ac/config.json:

{ "backend": "sounddevice" }

When using JACK, the server must be running before any measurement:

jackd -d alsa -d hw:0 -r 48000 -p 1024 -n 2

Quick start

ac devices                          # list available audio ports
ac setup output 11 input 0          # tell ac which channels to use
ac calibrate                        # interactive level cal (enables dBu)
ac plot 20hz 20khz 0dbu 20ppd show  # measure THD vs frequency, open plot
ac s f 20hz 20khz 0dbu              # fast output-only chirp
ac m sh                             # live spectrum, pyqtgraph window

Commands

Command	What it does
devices	List audio ports
setup	Configure hardware — output, input, reference, range, dmm, gpio
calibrate	Interface calibration
generate	Play a sine or pink noise tone
sweep	Level ramp or frequency chirp
plot	Point-by-point THD measurement with PNG output
transfer	H1 transfer function (magnitude, phase, coherence)
monitor	Live spectrum with TUI bar chart
probe	Auto-detect analog ports and loopback pairs (DMM + capture scan)
dmm	One-off AC Vrms reading from SCPI multimeter
server	Enable/disable server, show connections, connect to remote
stop	Stop active generator/measurement

Units

Everything is positional. The suffix tells ac what it is:

Suffix	Meaning	Examples
hz khz	Frequency	20hz 1khz 20000hz
dbu dbfs vrms mvrms vpp	Level	0dbu -12dbfs 775mvrms 1vrms 2vpp
s	Duration / interval	1s 0.5s
ppd	Points per decade	10ppd 20ppd

Append show to any command to open a pyqtgraph window.

Abbreviations

Everything has a short form:

s(weep)  m(onitor)  g(enerate)  c(alibrate)  p(lot)  tf/tr(ansfer)  pr(obe)
l(evel)  f(requency)  si(ne)  pk(ink)  sh(ow)
se(tup)  d(evices)  st(op)  ref(erence)

Sessions

Group measurements into named sessions:

ac new myamp        # create + activate
ac sessions         # list all
ac use myamp        # switch
ac diff amp1 amp2   # compare

GPIO — physical button control

Optional hardware interface for hands-free operation. A usb2gpio board (Arduino Mega2560) connects via USB serial and provides physical buttons for starting/stopping tone generation, with LED feedback for active state.

Buttons trigger ZMQ commands to the server — press SINE to generate a 1 kHz tone at the calibrated level, press STOP to silence it. LEDs reflect what's playing.

ac setup gpio /dev/ttyUSB0   # enable
ac setup gpio none           # disable
ac gpio                      # show status
ac gpio log                  # stream button events

The server auto-starts the GPIO handler on launch if gpio_port is configured.

DMM — automated meter readings

Optional SCPI integration for reading a bench multimeter (e.g. Keysight 34461A) over TCP. During calibration, ac queries the DMM for AC Vrms readings instead of requiring manual entry — it connects to port 5025, sends MEAS:VOLT:AC?, and averages three readings.

The DMM value is presented as a suggestion; you can accept it or type an override.

ac setup dmm 192.168.1.100   # enable (IP or hostname of meter)
ac setup dmm disable          # disable
ac dmm                        # take a one-off reading
ac calibrate                  # uses DMM automatically if configured

Server

ac is client/server — the server manages audio I/O and runs analysis. It auto-spawns locally. For remote use:

ac server enable          # bind to all interfaces on a server
ac server 192.168.1.5     # connect to remote server

Dependencies

numpy, scipy, matplotlib, sounddevice, pyzmq. Optional: jack-client (for JACK backend), pyqtgraph (for live GUI views).