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spxlAudioToMidi v08

by subpixel,


Note: The description here may not properly match the old version (v08) in this directory, and is here is a guide. Refer to the source code in the zip for proper details!

A small application made with Processing to produce MIDI control messages from a live audio feed. Auto-levelling frequency band meters are used to obtain "peak" output values across the entire audio spectrum analysed (whereas it is usual to have strong bass response with weaker treble response), and easing is applied to make the levels less erratic. 10 separate monitor outputs are supplied, where each monitor is attached to one of the frequency band meters and that meter's output is scaled to the particular output range for the monitor, allowing for a reduced final output range as well as inverted ranges. Controls are provided to select the MIDI output device and the MIDI channel to use, as well as for selecting which monitors are connected to which meters and the monitor output ranges.

This app has been used to control VJ applications Resolume and Neon v2, allowing simultaneous control from an external MIDI controller on the same channel (using loopMIDI as a virtual MIDI driver and MIDI-OX for routing).

Monitoring audio on Windows 10

The "Stereo Mix" device has been removed from Windows 10. To do monitoring in Windows 10 now requires a hacky workaround using a 3rd party driver. See How to Get Stereo Mix in Windows 10. Unfortunately, this version of the app only looks for the mixer named "Stereo Mix", so you will need to rebuild it if you want to find a virtual audio device.


spxlAudioToMidi v08 (2014-06-08): developed and tested with Processing 2.0.3 under Windows 7 Professional (64-bit); re-built (2016-09-10) with Processing 2.2.1 under Windows 10 Professional (64-bit).

You can also check the file list.

Libraries used

Note: The "local copy" of is for Processing 3 and may not work with Processing 2.

LibraryPurposeLocal copy
Minim Audio analysis (FFT) (18MB)
proMIDI MIDI input/output (132KB)

Demo Videos

Note: These videos are from an earlier version running on Windows 7. The appearance and operation is similar in this version.


Special keys: F3 = sample audio from "Microphone" mixer and F4 = sample audio from "Stereo Mix" mixer can only be used once each time the app is run due to an unsolved problem. Also, choose the MIDI channel (the numbers at the top left of the window) before selecting the MIDI device, since there is some separate problem with re-opening the MIDI devices.

The text at the top of the window controls the MIDI output. The left column of 30 bars are audio meters; each meter representing an average for a frequency band produced by FFT analysis with the low frequencies at the top of the display and the high frequencies at the bottom of the display. The meters are auto-levelling and provide normalised output values between 0 and 1 (inclusive). The right column of 10 bars are meter monitors, with each one connected to a particular meter. A monitor's output value is determiend by scaling the input meter value over the monitor's output range between 0 and 127 (inclusive); the lower and upper limits of each range can be adjusted, including to scale the meter input inversely, and the meter it is connected to (thus the frequency band it monitors) can be changed. If a MIDI output device is selected, each time a monitor output value changes, the value is emitted as a MIDI control message on the selected output channel. The control number is in the range 1 to 10, with the top monitor being control 1 and the bottom one being control 10.

Selecting MIDI output device

Click on the "SELECT OUTPUT" text to pop up the "SELECT DEVICE:" menu. Click a displayed device to select. Subsequently, clicking a displayed device name presents the "SELECT DEVICE:" menu again, and clicking the displayed channel number presents a "SELECT CHANNEL:" menu with channels 1 to 16.

Adjust monitor output ranges

Each monitor ouutputs values in the range 0 to 127 (inclusive) by default. The "minimum" and "maximum" limits can be adjusted by clicking (and dragging) the monitor output bar. Clicking in the top 3/4 of the bar adjusts the maximum; clicking in the top 1/4 of the bar adjusts the minimum. When dragging, if the mouse is dragged above or below the bar, the limit being dragged (min or max) snaps back to the previous value. Right-click the bar to reset to the default full range (0 to 127).

Changing monitor links

When the mouse is just off the left edge of a monitor bar the link to the associated meter is hilighted and "Drag to meter" is displayed. Click and drag the mouse pointer, releasing over to the desired meter; releasing when not over a meter leaves the link as it was previously. Right-clicking when "Drag to meter" is shown resets the link to the meter assigned by default when the application was started.

Keyboard controls

The "selected monitor" refers to the monitor that the mouse is over.

Space / P
[P]ause (and unpause)
[M]ute meter inputs
Toggle [E]asing of meter values (on by default)
Reset [E]asing amount
Up / Down
Increase / Decrease easing amount
[ / ]
Decrease / Increase input MIDI CC and note offsets
Reset the meter [L]evels
Randomise link (to meter); Shift+Q for all monitors
Reset link (to default meters); Shift+A for all monitors
[F]lip range (swap min and max output values); Shift+F for all monitors
In[V]ert range (sets min to 127-min, max to 127-max); Shift+V for all monitors
[R]andom range (sets min and max output values); Shift+R for all monitors
Re[S]et range to default (sets min to 0, max to 127); Shift+S for all monitors
1 2 3 4 5 6 7 8 9 0
Set MIDI output channel (channels 1 to 10 only, 0 for channel 10)
! @ # $ % ^ & * ( )
Set the the MIDI input channel (channels 1 to 10 only)
Toggle display of values in [H]exadecimal
Toggle display of meters
Toggle display of monitors
Analyse "Microphone" input
Analyse "Stereo Mix"


Note: These screenshots are from an earlier version running on Windows 7. The appearance and operation is similar in this version.

Default state

Select MIDI device

Link to meter part 1

Link to meter part 2

Hover to show value

Set max output
Click (and drag)

Set min output
Click (and drag)

Random links,
random output ranges

Select MIDI channel

Pause + mute