Build an Airplay Receiver Using Raspberry Pi

If you’re like me, you have tons of music on your computer but usually end up listening to it on headphones. If you want to use real speakers, you either run an audio cable to your stereo (tripping hazard, low-quality sound) or drag out an audio interface ($$, lots of cables). Bluetooth is an option, but the sound quality is ok at best. Apple’s Airplay goes over wifi and gives much higher-quality audio, but you’ll need some way to get that signal to your receiver or amplifier. There are lots of options on the market, but if you have a Raspberry Pi lying around, it makes a great and very cheap solution!

I decided to use the HDMI out for audio, which gives way better quality, and to include a power button and LED inside a nice laser-cut case. So far, it’s worked great for music as well as movies and podcasts!

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Simple VU Meter Circuit


I recently bought a cheap VU meter on Amazon, which looks very cool but needs some circuitry to get running. Unlike vintage meters, which can be driven by the audio signal directly, newer (and especially cheap) meters require DC current. A simple circuit, based on this example by Rod Elliott, uses four diodes to convert the AC audio signal into DC, plus a resistor and capacitor to dampen the movement of the needle.

See Rod’s post for lots more technical detail and a more complex driver circuit. Of course, this is pretty lo-fi and not studio-quality equipment… it also didn’t cost $1000.

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More Audio Sample Sorting

Audio samples, sorted by numerical value with lines drawn between their initial and resulting positions in the recording.  Click on images for full-size (quite large).

Installing ffmpeg (and LAME) on Mac Snow Leopard and Lion

A video still created programmatically; thousands of these can be combined into video using the ffmpeg library – faster and cleaner than a clunky Final Cut project

UPDATE 2: I ran into an error trying to install ffmpeg using these instructions yesterday.  However, installing using MacPorts worked like a charm! I suggest following the instructions for installing LAME first, then use MacPorts to install ffmpeg using the following command:

UPDATE: Having switched recently to Lion, the install below didn’t quite work.  With a small tweak, it appears to be ok – see below for details.

Well, it might not be Lion (doing live musical performance with my laptop makes me leary of new operating systems) but after finding little recent info on installing ffmpeg on a Mac, I’ve put together this basic outline.  For someone who isn’t great at installing libraries using Terminal, it wasn’t completely straightforward, but it works!  You will need the Apple Developer Tools to make this work (so far as I can tell).

UPDATE: I did a fresh install of XCode and had to do one small addition to get everything to compile.  For details, see this post.

This tutorial is based on the tutorial by Stephen Jungels, with some explanation and consolidation targeted at noobs (like myself).  Definite hat tip, Stephen!

The basic steps are as follows, full details after the break:

  1. Install Git
  2. Download LAME
  3. Download ffmpeg
  4. Find or create folder to install to
  5. Install LAME
  6. Install ffmpeg
  7. Test

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Physical Samples

Doing some Friday afternoon math about the audio files on my computer.

~22 days of music = 80,129,302,838 samples*
Sample values range from -32,768 – 32,768

If each value were to be cut using a standard CNC mill with 0.000125″ accuracy, the resulting object would be:

10,016,162.8″ = 834,680.2′ = 158.08 miles long, and only…
8.192″ tall!

* calculation from Adam Caprez at the Holland Computing Center; thanks Adam!

Digital audio best practices

I recently found this .pdf by the CDP Digital Audio Working Group titled “Digital Audio Best Practices”.  It caught my eye because it was a great glossary of digital audio terms (perfect for my students).  It turns out it also has a good discussion of archival storage of digital audio.  I’ve been working on a “best practice” for my own studio (what sample rate to record new works at, how to store finished works, backups, etc) and this is another great piece of advice.

Via: Bibliographical Center for Research (BCR)