Tutorial 2: Delay Based Effects

Tutorial 2: Delay Based Effects

In this section, we define a function to create echo effect on input audio. Echo can be modeled as attenuated, delayed copies of the original signal added to itself. Here, it can be seen as an FIR filtering operation. The FIR filter we constructed is of form [1, delayed_sec*Fs-1, a], where delayed_sec is the number of seconds for the echo to arrive and a: 0<a<=1.

We can also make the amount of delay a function of time to make more interesting effects, such as flanger. The following function implements the flanger effect using a triangular function for time-varying delay, shown in the figure below..

Source code and test audio file: tutorial2

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An Unofficial Port of Matrix HAL to Ubuntu 22.04 and Raspbian Bullseye

What is Matrix VOICE and Matrix HAL?

The Matrix VOICE is described on the Matrix website as a “development board for building sound driven behaviors and interfaces.” It is a nifty piece of hardware that features an 8-microphone array and has unique possibilities for beamforming and audio processing applications.

However, in February 2021, when Matrix Labs was bought out, development and support for the Matrix VOICE C++ library, the Matrix HAL, was silently withdrawn.

The latest release of Matrix HAL only works with a version of the Raspberry Pi OS called Raspbian Buster which is fine for a lot of applications, but recently our research has been focused on integrating this device with ROS, a robotics framework that is meant for Ubuntu. While there were workarounds for using ROS on Raspbian Buster, this would not be without its own unique set of challenges.

It was determined that it would be valuable to investigate patching the Matrix HAL to work on Ubuntu 22.04. And over the summer, we were able to accomplish this goal.

Description of the Port

There are some limitations to the port. With our own acoustic research being the primary application, we did not ensure the functionality of sensors other than the microphone array. This means there is currently no support for the humidity sensor, IMU, pressure sensor or UV sensor. There is currently only support for the microphone array and the Everloop LED interface.

Additionally, the repo has not been tested on the Matrix CREATOR and there is no guarantee that it will be compatible with this patch.

You can download the source from this Github repository. Please direct any support related inquiries to gfw3@illinois.edu.

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