Testing audio output

Recording/Analyzing Signals

• Easiest: just write a binary output file. The Audacity audio editor can "Import Raw" audio. Select the correct format and import. Audacity is installed on all CCRMA machines or can be downloaded for free here. You will automatically view the time domain signal. To see the frequency response, you can select a portion of audio and click Analyze->Plot Spectrum.

Reference Signals

When creating signal generators yourself, you will want to compare your audio output to reference signals. Here are a few audio programing languages/environments that might be useful.

• Chuck-audio programming language (suggested for ease-of-use)

• Pure Data- a graphical audio programming language

• SuperCollider-audio programming language

• Bit Harder: use libsndfile(C library for reading and writing files containing sampled sound) to write an output file

SAMPLE CHUCK CODE

   // Comment/uncomment the different oscillators to hear each 

   SinOsc s => dac;
   //TriOsc s => dac;
   //SqrOsc s => dac;
   //PulseOsc s => dac;

  .2 => s.gain;

   while( true )
   {
       440.0 => s.freq;
       100::ms => now;
   }

   // Use this for impulse

   //Impulse i => dac;
   //while( true ) {
   //    1.0 => i.next;
   //    100::ms => now;
   //}

   // Use this for noise 

   //Noise n => dac;
   //.2 => n.gain;
   //while( true )
   //{
   //    100::ms => now;
   //}

Download and install. From there you'll need to create a small bit of code to make the same output signals.