This is a tool for measuring end-to-end MIDI synthesizer latency.

Disclaimer: This is not an official Google product.

It works with any Device Under Test (DUT) including Android and iOS with any
synthesizer app, Linux, Windows, macOS, and hardware synthesizers which can take
USB MIDI as input. The only connections which are required is analog audio into
the Teensy and a USB connection to the DUT. Note that the Teensy is set to
operate in gadget mode, so mobile devices will require an OTG cable or
equivalent.

The tool is based on WALT (https://github.com/google/walt) but uses different
software. The audio portion is the same as WALT, so please refer to the
schematic provided in the hardware folder of the repo. In addition, it requires
an I2C controlled LCD such as one that uses a SainsmartLCD2004 controller. This
is the one that I used:
https://www.amazon.com/SainSmart-Module-Arduino-Board-White/dp/B003B22UR0.
Connect SDA0 and SCL0 to the respective pins on the LCD. Also connect these
signals to 3V3 via a 3.3K pull-up resistor. GND on the LCD connects to GND on
the Teensy and VCC goes to Vin assuming the Teensy is powered over USB.

See the note in the arduino directory of that repo for help setting up your
compilation environment.

This tool works by generating MIDI noteOn messages over USB and measuring how
long it takes for the DUT to produce sound above a certain threshold in
response. This means that voices using a strong attack such as percussion are
ideal and the volume on the synthesizer should be set to the maximum level.

The results are summarized on the LCD but exporting of raw data is currently not
implemented.