Quick Project: D3 / HTML5 Web Audio Spectrum Analyzer

For fun this last week I made a spectrum analyzer using D3 and the HTML5 Web Audio API.  Been meaning to check those out for a while, and spectrum analyzer seemed like the natural way to kill two birds.

Here it is running on Heroku with some of my music as the example track

http://d3-spectrum.herokuapp.com

And the github page here:

https://github.com/arirusso/d3-audio-spectrum

Increasing the curve setting gives the spectrum a more logarithmic display, traditionally more common for audio spectrum analyzers.

The other controls are pretty straightforward

Enjoy

Updates:
Adding live audio input in Chrome Canary (10/4/2012)

Quick Project #2: Ruby Methods for Protecting Against Timing Attacks

Breaking with my usual style, Quick Project #2 doesn't necessarily relate to music programming.

Today I came across a nice little article and demo on r/compsci about timing attacks.

Timing attacks are something that I had learned about a few years ago but for whatever reason had dropped from the forefront of my engineering consciousness. In order to bash myself over the head with it (and provide a universal solution), I created Ruby wrapper methods for Object#send and block evaluation that are padded with a fixed timing delay.

Here 'tis, including some basic String comparison examples at the bottom:

https://gist.github.com/2554841

To use it, just pass in a "safe" duration (in seconds) that likely exceeds any possible amount of time it could take to evaluate the code. In the following example I use the greatly exaggerated value of .75 seconds. In the wild, you'll most likely be working in smaller durations

  is_match = ExpressionTimer.block(0.75) { "password attempt!" == "my password!" }

When the example is run, no matter how quickly the block actually evaluates, it will always take exactly 3/4s of a second to return. As a result, actual timing information is lost in the ether and can not be gleaned by any outside observer.

Quick Project #1: Extract Audio Samples From Online Video

As I get ready to move once again (this time to the Ridgewood/Bushwick border) there's not a whole lotta time for personal projects. Yesterday I decided that I would find a quick one and do it no matter how useless it was.

Turned out, I came up with something that's going to be pretty useful (for me). Last week, a coworker pointed me to marcel's awesome Ruby giftube script which extracts animated gifs from online videos. I've been looking to incorporate more audio samples in my music for quite some time, so I forked his script and changed it to extract audio samples instead of gifs, complete with mp3 conversion.

Here's the result:

https://gist.github.com/2473383

MicroOSC: a Ruby DSL for OSC

Being on my way to the west coast and out of arm's reach of the synths, I've had a few hours to switch gears and put together a quick Ruby gem, MicroOSC. It's a utility and DSL for dealing with OSC messaging.

gem install micro-osc

I applied the same principle to OSC that I applied to MIDI with MicroMIDI: distilling the simplest messenger interface that I could think of.

Unlike MIDI, OSC deals with generic user-defined messages. This eliminates the need for describing different concrete message types, something that added a lot complexity to MicroMIDI.

MicroOSC can function as a server, a client or both. In this example, I'll demonstrate them separately, having the two programs talk to each other over a local network.

Here is a server:

require "osc"

OSC.using(:input_port => 8000) do

  receive("/greeting") { |val| p "received #{val}" }

  p "Ready to receive OSC messages on port(s) #{input_ports.join(', ')}..."

  wait_for_input

end

Once you have this running, you should see "Ready to receive OSC messages..." in your Ruby console. Switch to another window and run this client program:

require "osc"

o = OSC.using(:output => { :host => "localhost", :port => 8000 })
o.out("/greeting", "hullo!")

After running it, flip back to your server program and see “received hullo!”, confirming that your two programs were in fact talking to each other!

Notice that in the second program I didn't use a Ruby block style. Doing it this way would generally be better for live coding, and probably some other scenarios as well.

That's it!

Look for another post with real-world examples, advanced techniques and combining with MicroMIDI soon.

http://github.com/arirusso/micro-osc

Shift

It's break time for my programming projects while I actually play and record some music.  I also started a new job with Paperless Post that I'm dedicating a lot of my programming energies to.

I'll post here soon when I have anything of note to show for what I'm doing.

Here's a video of me on some hardware synths that a friend posted last year. It sounds somewhat similar to what I'm doing now.



I can never stay away too long; I'm sure I'll be back to grinding out some music tools once I have a few tracks done. Just not enough time for both at the moment...

OSC Access: Build OSC into Ruby objects

I've created a Ruby library called OSC Access for binding OSC directly into Ruby classes and objects.

It conveniently wraps a lot of functionality from osc-ruby, handling server/client sharing and management as well as other tasks commonly associated with OSC.

gem install osc-access

All of OSC Access' functionality is available by including the OSCAccessible module into a class. The module gives you a lot of functionality but you'll want to know about these three methods in particular to get up and running

• osc_receive
• osc_send
• osc_start

osc_receive

All OSC input is handled by using the osc_receive method. Here's an example of using osc_receive in a simple way:

class Instrument

  include OSCAccessible

  osc_receive("/1/fader1") do |instance, val|
    instance.velocity = val
  end

  def velocity=(val)
    puts "setting velocity to #{val}"
    ...
  end

end

i = Instrument.new
i.osc_start(:input_port => 8000).join

When this example is run, the method velocity= is called on all instances of the Instrument class whenever OSC messages for the address /1/fader1 are received.

A couple of things to note here...

In order to enable OSC input, an input port must be specified for each instance. I've done that in this example using the osc_start method but there is also a method osc_input which just takes a port number. You can also add multiple input ports and share ports across various objects. (see example...)

Another thing to note is that val is, by default, the value of the first argument of the received OSC message. (OSC messages can have an unlimited number of arguments). You can modify which arg is used, or pass in all of them, by setting the :arg option on osc_receive.

You can also use osc_receive as an instance method. (see example...) However, more usefully, you can create a Hash map spec of osc_receive calls and pass it to an instance like this:

map = {
  "/1/fader1" => { 
    :translate => { :remote => 0..1, :local => 0..127 }
    :action => Proc.new { |instance, val| instance.pitch = val }
  }
}

class Instrument

  include OSCAccessible

  def pitch=(val)
    puts "setting pitch to #{val}"
    ...
  end

end

i = Instrument.new
i.osc_start(:map => map, :input_port => 8000).join

This kind of approach gives you more flexibility by decoupling the OSC spec for your object from the class -- like a controller and model in MVC.

Osc_receive has a few options:

:translate

There's another difference between those two examples: the :translate option means that val will be translated from a number between 0 to 1 to the analogous value between 0 and 127 before being passed to the code block. So for example if the first argument of the received OSC message is equal to 0.5, val will be equal to 63.

:thru

By setting the :thru option to true, any messages that are received for /1/fader1 are sent immediately to the output (as well as calling the :action block). For example, using the Instrument class from the last example:

map = {
  "/1/fader1" => { 
    :thru => true
    :translate => { :remote => 0..1, :local => 0..127 }
    :action => Proc.new { |instance, val| instance.pitch = val }
  }
}

i = Instrument.new
i.osc_start(:map => map, :input_port => 8000, :output => { :host => "192.168.1.9", :port => 9000 }).join

As you can see, I also specified an OSC output host and port for this example. If you're ever missing input or output port or host info, your object simply will not perform IO -- it won't raise any kind of exception.

osc_send

Osc_send gives you the ability to output arbitrary OSC messages. The first argument is the address of the message and any arguments after that are the content. Here is an example of our class definition from this first example with output added

class Instrument

  include OSCAccessible

  osc_receive("/1/fader1") do |instance, val|
    instance.velocity = val
    instance.osc_send("/velocity", val)
  end

  def velocity=(val)
    puts "setting velocity to #{val}"
    ...
  end

end

i = Instrument.new
i.osc_start(:map => map, :input_port => 8000, :output => { :host => "192.168.1.9", :port => 9000 }).join
i.osc_send("/greeting", "hi!")

In this example, I'm sending a message from both osc_receive's action block and in the main program block after i is instantiated.

osc_start

Osc_start starts all of the OSC servers that are connected to your objects. You must call it on an instance before osc_receive will function.

I'll be adding OSC Access to Diamond and coming up with a way to use it with MicroMIDI in the next few days. Thanks for reading.

http://github.com/arirusso/osc-access

Selecting a MIDI Device With Unimidi

There are a couple of recent changes to how MIDI devices can be selected with Unimidi.

Prompting the User

The first is the addition of a handy console prompt that asks the user to select a device and waits for input.  The code looks like this

require "unimidi"

@input = UniMIDI::Input.gets

on my computer, this results in

Select a MIDI input
1) IAC Device
2) Roland UM-2 (1)
3) Roland UM-2 (2)
> 

Note that when the user makes a selection, the device is returned enabled so you don't need to call @input.open on it.

Hard Coded

There's also been some changes to how hard coded selection can be done. As with the user prompt, now you can select and open a device at one fell swoop. Here's a couple of examples which both open the same output. (Device#use and Device#open are the same)

@output = UniMIDI::Output.open(0)
@output = UniMIDI::Output.use(:first)

And of course, you can select and open the device separately if you wish

@input = UniMIDI::Input.all[0].open
@input = UniMIDI::Input.first.open

A Note About Live Coding in IRB with OSX

Apparently some versions of readline for OSX cause IRB to block thread-passing while it's waiting for user input at the prompt.

If you're experiencing problems live coding in IRB, such as starting the Diamond arpeggiator and nothing happening, it could be because of this. Unfortunately, as far as I know, the only way to fix it is to disable readline. You can do this by adding this line to ~/.irbrc

IRB.conf[:USE_READLINE] = false

This is annoying, because then you'll no longer have the ability to recall previously used commands and things like that. I've been meaning to get text editor based live coding up and running so maybe this is the time

More MicroMIDI Tricks

MicroMIDI has a few less obvious features that may be useful once you have the basics down.

Sans block

In addition to how I worked in the other examples, MicroMIDI can be used outside of the context of a Ruby block. This allows you to integrate it as a more conventional Ruby library.

Here is the first example from this post redone without a block

@o = UniMIDI::Output.use(:first)

midi = MIDI::IO.new(@o)

midi.note("C")
midi.off 

midi.cc(5, 120)

midi.play("C3", 0.5)

Note that you can also re-open the IO object in a block later using the edit method

midi.edit do 
  play "G3", 1
end

Performance Shortcuts

There are also performance shortcuts that generate messages based on past messages or common conventions.

• off - this generates a note-off message based on the last note-on message created
• quiet! - sends note-off messages to all MIDI channels on all outputs
• repeat - generates a copy of the last message created

Super Sticky Mode

Again in this post, I explained how MicroMIDI uses sticky values. There is also a super sticky mode that allows you to change the values inline with each message you create. Here's an example:

MIDI.using(@o) do

  super_sticky

  channel 1

  note "C4"
  off

  octave 5
  velocity 60

  note "E", :channel => 2
  off

  note "C3"
  off

end

When this program is run, these messages are sent to @o:

* note C4 (channel 1, vel 100)
* note-off C4 (channel 1, vel 100)
* note E5 (channel 2, vel 60)
* note-off E5 (channel 2, vel 60)
* note C3 (channel 2, vel 60)
* note-off C3 (channel 2, vel 60)

As you can see, when I sent :channel => 2 to the second note command, the MIDI channel remained for the commands that followed rather than just being transient for that command.

Message Cache

MicroMIDI keeps a timestamped log of the messages you create. You can access this log using the cache command, like this:

M do
  note "C4"
  cc 5, 120
  play "C2", 3
  
  puts cache
end

This code gives you this output:

{ :message=>#<MIDIMessage::NoteOn:0x007fbb6092baf8 
    @const=#<MIDIMessage::Constant:0x007fbb60930eb8 @key="C4", @value=60>, 
    @status=[9, 0], 
    @data=[60, 100], 
    @channel=0, 
    @note=60, 
    @velocity=100, 
    @name="C4", 
    @verbose_name="Note On: C4">, 
  :timestamp=>2.513885498046875 
}

{ :message=>#<MIDIMessage::ControlChange:0x007fbb60924e10 
    @const=#<MIDIMessage::Constant:0x007fbb6093df00 @key="Portamento Time", @value=5>, 
    @status=[11, 0], 
    @data=[5, 120], 
    @channel=0, @index=5, 
    @value=120, 
    @name="Portamento Time", 
    @verbose_name="Control Change: Portamento Time">, 
  :timestamp=>2.7201175689697266 }

{ :message=>#<MIDIMessage::NoteOn:0x007fbb60921558 
    @const=#<MIDIMessage::Constant:0x007fbb60931f48 @key="C2", @value=36>, 
    @status=[9, 0], 
    @data=[36, 100], 
    @channel=0, 
    @note=36, 
    @velocity=100, 
    @name="C2", 
    @verbose_name="Note On: C2">, 
  :timestamp=>2.961874008178711 
}

{ :message=>#<MIDIMessage::NoteOff:0x007fbb60917c38 
    @const=#<MIDIMessage::Constant:0x007fbb60931f48 @key="C2", @value=36>, 
    @status=[8, 0], 
    @data=[36, 100], 
    @channel=0, 
    @note=36, 
    @velocity=100, 
    @name="C2", 
    @verbose_name="Note Off: C2">, 
  :timestamp=>3003.7591457366943 
}

http://github.com/arirusso/micromidi

Generating Sysex Messages with MicroMIDI

Recently, the idea of converting MIDI Control Change messages to Sysex on the fly has come up a couple of times. One could use this to control a synth such as a Roland MKS or Yamaha DX7 that only accepts Sysex for control with a regular MIDI knob controller.

The following is a simplified example of doing this with MicroMIDI.

@i = UniMIDI::Input.use(:first)
@o = UniMIDI::Output.use(:first)
  
MIDI.using(@i, @o) do
  
  node :roland, :model_id => 0x42, :device_id => 0x10
  
  *@my_map =
    [0x40, 0x7F, 0x00],   
    [0x41, 0x7F, 0x00],
    [0x42, 0x7F, 0x00]
  
  receive :cc do |message|
      
    command @my_map[message.index - 1], message.value
      
  end
  
  join
  
end

Defining a Node

I won't get into too much background on Sysex but there are two concepts that one must understand in order to generate Sysex with MicroMIDI.

The first concept is what I call a Sysex Node: there are up to three bytes of data used in each Sysex message to identify the synth/module/destination/node/etc where the message is intended to be sent. This is not unlike the MIDI channel in a regular short message except that it's three bytes. Two of those bytes pinpoint the make and model of the synth while the third byte identifies the individual synth (device ID) in case you have multiple Yamaha DX7's or whatever the case.

MicroMIDI allows you to define these bytes as a sticky value using the node function.

Since I'm only using one synth for the entire example, I call the node function before setting up the input event to catch Control Change messages. (If you are using multiple synths and multiple events you would call node in each event block). The arguments represent the Manufacturer ID and the optional Model ID and Device ID. The Manufacturer can be referred to by a symbol (as above) or a string if its name is found in the manufacturer constants in midi.yml (by all means, add yours and do a pull request).

Now here's the annoying part: different brands and synth models use this Node data differently. For instance, I believe some devices don't understand messages with a model ID in them. In those cases just leave out whatever needs to be omitted from your messages. As I learn more about this myself, perhaps I can have this function streamline accepting the proper data for major synth types.

Command vs Request

The other concept to understand is that Sysex messages can (in theory) either be a command or request. This is pretty simple, and if you are creating a controller program you'll deal mostly in commands. In the case of the example above, we send a command

command @my_map[message.index - 1], message.value

When using the command function, the first argument is the sysex address and the second is the value to assign. The value can either be a number, as in this case, or an array of bytes. When making a request, the first argument is also the address but the second argument is the size of the response (in bytes) that you expect to receive

request 0x43, 43

If all else fails...

Due to the fact that Sysex hasn't had a truly concrete spec, some devices will use messages that don't really adhere to the command/request format. In those cases, you can just use the generic sysex command like this

sysex 0x1, 0x2, 0x3, 0x4

With no node specified, this will give you a message composed of

F0 01 02 03 04 F7

In other words, sysex will create a message and not perform any validation or add a checksum to it. You can still use node with these message-- it will append those bytes immediately after the F0 start byte as it would with a command or request.

tldr, Sysex is tricky to to objectify

If you'd like to gain a deeper understanding of how sysex messages work, this is a good tutorial (if Roland-centric) and I often referred back to it while creating MicroMIDI and the libraries that support it.

http://github.com/arirusso/micromidi

Next: More MicroMIDI Tricks