PortAudio

With the ability to run a full Linux operating system, the Intel Edison board has more than enough computing power for real-time digital audio processing. [Navin] used the Atom based module to build Effecter: a digital effects processor.

Effecter is written in C, and makes use of two libraries. The MRAA library from Intel provides an API for accessing the I/O ports on the Edison module. PortAudio is the library used for capturing and playing back audio samples.

To allow for audio input and output, a sound card is needed. A cheap USB sound card takes care of this, since the Edison does not have built-in hardware for audio. The Edison itself is mounted on the Edison Arduino Breakout Board, and combined with a Grove shield from Seeed. Using the Grove system, a button, potentiometer, and LCD were added for control.

The code is available on Github, and is pretty easy to follow. PortAudio calls the audioCallback function in effecter.cc when it needs samples to play. This function takes samples from the input buffer, runs them through an effect’s function, and spits the resulting samples into the output buffer. All of the effect code can be found in the ‘effects’ folder.

You can check out a demo Effecter applying effects to a keyboard after the break. If you want to build your own, an Instructable gives all the steps.

Continue reading “Audio Effects On The Intel Edison” →

[Pekka] set himself up with quite the challenge – use an oscilloscope screen to display Quake in realtime – could it even be done? Old analog scope screens are just monochromatic CRTs but they are designed to draw waveforms, not render graphics.

Over the years Hackaday has tracked the evolution of scope-as-display hacks: Pong, Tetris, vector display and pre-rendered videos. Nothing that pushed boundaries quite like this.

[Pekka]’s solution starts off the same as many others, put the scope in X-Y mode and splice up your headphone cable – easy. He then had to figure out some way to create an audio signal that corresponded to the desire image. The famous “Youscope” example demos this, but that demo is pre-rendered. [Pekka] wanted to play Quake in realtime on the scope itself, not just watch a recording.

With only so much bandwidth available using a soundcard, [Pekka] figured he could draw a maximum of about a thousand lines on screen at a time. The first headache was that all of his audio cards had low-pass filters on them. No way around it, he adjusted his ceiling accordingly. ASIO and PortAudio were his tools of choice to create the audio on the fly from a queue of XY lines given.

To tell his audio engine what lines to draw, he solicited Darkplaces – an open source Quake rendering engine – and had it strip polygons down to the bare minimum. Then he had to whip out the digital hedge trimmers and continue pruning. This writeup really cannot do justice to all the ingenious tricks used to shove the most useful data possible through a headphone jack. If this kind of thing interests you at all, do yourself a favor and check out his well-illustrated project log.

In the end [Pekka] was not entirely happy with the results. The result is playable, but only just barely. The laptop struggles to keep it simple enough, the soundcard struggles to add enough detail and the scope struggles to display it all quickly enough. At the very least it sets the bar extraordinarily high for anyone looking to one-up him using this method. There is only so much water that can be squeezed from a rock.

See the video below of [Pekka] playing the first level of Quake.

Continue reading “Ultimate Oscilloscope Hack – Quake In Realtime” →