Jackson’s Status Report for 2/27

This week, I familiarized myself with the Web Audio API. This is crucial to our project since it deals with in-browser audio processing, and none of us have experience with that sort of thing. Though I’ve done a lot of audio DSP, I’ve never used the web APIs meant to do that. What I’ve learned is that it’s actually quite simple, and fairly similar to Nyquist, though a lot less elegant. Audio elements such as sound sources, oscillators, filters, gain controls, etc. are all built into your browser already, and all you have to do is route them all properly.

Following a number of different tutorials, I made a few different small in-browser audio applications. I ran them on a Django server I created with a single view pointing to a url, which loads an html file. This html file loads some javascript, which is where I did most of my work. This post contains some code snippets of interest that make up a small portion of code that I wrote this week.

Firstly, I created a small synthesizer, which generates white noise on a button press with a simple for loop:

The channelData is connected to an audio buffer called “buffer”, which is routed to a gain node before being sent to your computer’s audio output. Generating a click track (which will be part of our final product) can be done in a similar way.

The white noise can be filtered in real time by inserting a biquad filter in between the buffer and the gain node. The syntax for this is very simple as well:

With some Web Audio API basics down, I moved on to the main thing our application needs to do in-browser, which is audio recording and playback. I created a small recorder, which saves CD quality audio in chunks (in real time), and after a set amount of time, it stops recording, creates a blob containing the recorded audio, and plays the audio back to the user. This recording interface was my deliverable this week, so I would say we are still on schedule.

For next week, I will integrate this recorder with the Django server we’re using for the final product, and hopefully get the recorded audio sent to the server. More than likely, I will write a new one from scratch, with the information I’ve learned this week.