[Andy] had the idea of turning a mixing desk into a MIDI controller. At first glance, this idea seems extremely practical – mixers are a great way to get a lot of dials and faders in a cheap, compact, and robust enclosure. Exactly how you turn a mixer into a MIDI device is what’s important. This build might not be the most efficient, but it does have the best name ever: digital to analog to digital to analog to digital conversion.

The process starts by generating a sine wave on an Arduino with some direct digital synthesis. A 480 Hz square wave is generated on an ATTiny85. Both of these signals are then fed into a 74LS08 AND gate. According to the schematic [Andy] posted, these signals are going into two different gates, with the other input of the gate pulled high. The output of the gate is then sent through a pair of resistors and combined to the ‘audio out’ signal. [Andy] says this is ‘spine-crawling’ for people who do this professionally. If anyone knows what this part of the circuit actually does, please leave a note in the comments.

The signal from the AND gates is then fed into the mixer and sent out to the analog input of another Arduino. This Arduino converts the audio coming out of the mixer to frequencies using a Fast Hartley Transform. With a binary representation of what’s happening inside the mixer, [Andy] has something that can be converted into MIDI.

[Andy] put up a demo of this circuit working. He’s connected the MIDI out to Abelton and can modify MIDI parameters using an audio mixer. Video of that below if you’re still trying to wrap your head around this one.

Control surfaces (input devices with sliders, encoders, buttons, etc) are often used in audio and video editing, where they provide an easy way to control editing software. Unfortunately even small control surfaces are fairly expensive. To avoid shelling out for a commercial control surface, [Victor] developed his own custom control surface that sends standard MIDI commands which can be interpreted by nearly any DAW software.

[Victor]‘s control surface includes several buttons, a display, and a rotary encoder. His firmware sends MIDI commands whenever a button is pressed or the rotary encoder is turned. [Victor] plans on adding menu functionality to the currently unused LCD display which will allow the user to change the scrubbing speed and other various settings.

One advantage of making your own control surface is that you can customize it to your own needs. [Victor] has posted a model of his 3d-printed enclosure and his source code on the project page so you can easily modify his design with any button configuration you might want.

[Florian Amrhein] made use of some old hardware to build his own internet radio in a 1930′s radio case.

The original hardware is a tube-amplified radio which he picked up on eBay. There’s tons of room in there once he removed the original electronics and that’s a good thing because he crammed a lot of new parts into the build. The main one being an old laptop he had on hand. It’s got a 10″ screen which is too large for the opening, but that ended up being okay. He coded an interface with C and SDL which give him a visual representation of his favorite online streams. The knob to the right moves the red line when turned and causes the Debian box to change to the new stream using the Music Player Daemon. Two potentiometers control the tuning and volume, and there is also a rotary encoder which is not yet in use. All three are connected to the laptop via an Arduino.

Check out the finished product in the video after the break. It sounds quite good thanks to the small automotive speaker and amplifier also crammed into the old case.

If you don’t have a laptop lying around to use in a project like this consider a microcontroller and character LCD based system.

Here [Matthew Br] explains the situation he’s in with the neighbors that share this wall of his apartment. When they listen to music they like it loud and so he gets to ‘enjoy’ the experience as well. But he can’t ignore it any longer, and has decided to use a sound volume detector to blast some tunes right back at them.

He taped a microphone to the wall and wired it up to his Arduino. It monitors incoming sound and, using an adjustable threshold, it will trigger when the neighbors are too loud. We think he was wise to include some time filtering that makes sure the loud noises are sustained and not just the result of someone bumping into the wall. When the system does detect loud music for a sustained period it triggers [Matthew's] own CD player to pump out Who Let the Dogs Out? by the Baha Boys. It will play for a period of time, then shut off to listen and see if the neighbors are still rowdy.

He documents an actual run in the latter half of the clip after the break. We sure hope he’s living in a building with just two units, otherwise this will drive the rest of the neighbors batty as well!