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Signal Estimator ================ [](https://github.com/gavv/signal-estimator/actions) <!-- toc --> - [Features](#features) - [Example use cases](#example-use-cases) - [Supported platforms](#supported-platforms) - [Dependencies](#dependencies) - [Installation](#installation) - [Graphical interface](#graphical-interface) - [Command-line options](#command-line-options) - [Measuring latency](#measuring-latency) - [Measuring losses](#measuring-losses) - [JSON output](#json-output) - [Dumping streams](#dumping-streams) - [ALSA parameters](#alsa-parameters) - [Real-time scheduling policy](#real-time-scheduling-policy) - [Acknowledgments](#acknowledgments) - [Authors](#authors) - [License](#license) <!-- tocstop --> Features -------- `signal-estimator` is a small command-line and GUI tool allowing to measure different characteristics of the signal looped back from audio output to audio input. Features: * send test signal to output device and receive looped back signal from input device * measure signal latency (the shift between output and input signal) * measure signal loss ratio (number of glitches per second in the input signal) * measurements output in JSON format for easy parsing * dump output and input streams to text files and plot them using matplotlib Example use cases ----------------- * Measure local hardware latency. *Example setups:* * connect computer's audio output to its audio input using a jack cable * place computer's speakers near the its microphone * Measure total latency and signal quality of an external hardware + software system. *Example setups:* * measure Raspberry Pi hardware + software latency connect computer's audio output to a Raspberry Pi's input and vice versa, and run a program on Raspberry Pi that loops back signal from input to output * measure hardware + software + network latency / quality of the two Raspberry Pies connected via a network transport connect computer's audio output to the first Raspberry Pi's input, and computer's audio input to the second Raspberry Pi's output, and connect the two Raspberry Pies using some network audio transport * measure the hardware + software + bluetooth latency / quality of a mobile phone with bluetooth microphone and headphones place computer's speakers near bluetooth microphone connected to a mobile phone, place computer's microphone near bluetooth headphones connected to the phone, and run a mobile app that loops back signal from bluetooth microphone to bluetooth headphones In these examples, you'll need to measure the latency of your local harware first, and then subtract it from the measurements results, to get the actual latency of the external system being tested. Supported platforms ------------------- * Linux / ALSA Dependencies ------------ * C++17 compiler * CMake >= 3.0 * libasound (ALSA devel) * Qt5 and Qwt (for GUI) Installation ------------ Install dependencies: ``` sudo apt install libasound2-dev qtbase5-dev libqwt-qt5-dev ``` Clone repo: ``` git clone --recurse-submodules https://github.com/gavv/signal-estimator.git cd signal-estimator ``` Build: ``` make ``` Build without GUI (in this case Qt and Qwt are not needed): ``` make no_gui ``` Install into the system (optionally): ``` sudo make install ``` Graphical interface ------------------- The tool comes with a simple GUI (`signal-estimator-gui`) that plots the signal in the real-time. It can be especially useful for troubleshooting problems with measurements. It uses Qt and Qwt libraries. Internally, it invokes the command-line tool (`signal-estimator`) and parses its output. Here is how it looks like: <img src="https://github.com/gavv/signal-estimator/blob/main/doc/screenshot.png" width="600" /> Command-line options -------------------- ``` $ ./bin/signal-estimator --help Measure characteristics of a looped back signal Usage: signal-estimator [OPTION...] General options: -h, --help Print help message and exit -f, --format arg Output Format: json|text (default: text) -m, --mode arg Mode: noop|latency|losses (default: latency) -o, --output arg Output device name, required -i, --input arg Input device name, required -r, --rate arg Sample rate (default: 48000) -c, --chans arg Number of channels (default: 2) -v, --volume arg Signal volume, from 0 to 1 (default: 0.500000) -p, --periods arg Number of periods in ring buffer (default: 2) -l, --latency arg Ring buffer size, microseconds (default: 8000) -d, --duration arg Measurement duration, seconds (default: 10.000000) Reporting options: --sma arg Simple moving average window in reports (default: 5) Latency estimation options: --strike-period arg Strike period, seconds (default: 1.000000) --strike-length arg Strike length, seconds (default: 0.100000) --strike-detection-window arg Strike detection running maximum window, in samples (default: 96) --strike-detection-threshold arg Strike detection threshold, from 0 to 1 (default: 0.400000) Loss ratio estimation options: --signal-detection-window arg Signal detection running maximum window, in samples (default: 48) --signal-detection-threshold arg Signal detection threshold, from 0 to 1 (default: 0.150000) --glitch-detection-window arg Glitch detection running maximum window, in samples (default: 32) --glitch-detection-threshold arg Glitch detection threshold, from 0 to 1 (default: 0.050000) File dumping options: --dump-output arg File to dump output stream --dump-input arg File to dump input stream --dump-frame arg Dump only one maximum value per frame (default: 64) --dump-rounding arg Round values before dumping and don't dump duplicates (default: 10) ``` Measuring latency ----------------- In the latency estimation mode, the tool generates short periodic beeps ("strikes") and calculates the shift between each sent and received strike. ``` $ ./bin/signal-estimator -m latency -o hw:1,0 -i hw:1,0 -d 5 opening alsa writer for device hw:1,0 suggested_latency: 8000 us suggested_buffer_size: 384 samples selected_buffer_time: 8000 us selected_buffer_size: 384 samples selected_period_time: 4000 us selected_period_size: 192 samples opening alsa reader for device hw:1,0 suggested_latency: 8000 us suggested_buffer_size: 384 samples selected_buffer_time: 8000 us selected_buffer_size: 384 samples selected_period_time: 4000 us selected_period_size: 192 samples can't enable real-time scheduling policy can't enable real-time scheduling policy latency: sw+hw 13.145ms hw 2.934ms hw_avg5 2.934ms latency: sw+hw 12.465ms hw 2.924ms hw_avg5 2.929ms latency: sw+hw 13.171ms hw 2.968ms hw_avg5 2.942ms latency: sw+hw 12.510ms hw 2.962ms hw_avg5 2.947ms latency: sw+hw 12.536ms hw 3.008ms hw_avg5 2.959ms ``` Notation: * `sw+hw` - total software + hardware latency, including ALSA ring buffer computed as the time interval beginning when the first audio *frame* of the strike was sent to the output ring buffer, and ending when the first frame of the strike was received from the input ring buffer * `hw` - an estimation of hardware latency, excluding ALSA ring buffer computed as the time interval beginning when the first audio *sample* of the strike was sent from ring buffer to DAC, and ending when the first sample of the strike was received from ADC and plac