Music and Computers

Sampled Fader

This Applet simulates the way that a Analog to Digital Convertor (ADC) samples a continuously changing value and produces a stream of numbers.  The vertical faders represents the analog signal coming from a microphone or mixer. The graphical display represents the sampled values coming from the ADC.

To Do:

  1. Move the fader slowly up and down. Notice that the samples reflect the fader's motion.
  2. Move the fader very slowly. Notice that the samples jump between levels even when the fader moves smoothly. This is called "quantization". Quantization can cause hiss in a digital recording. In this example we are quantizing to 5 bits which only gives us only 32 levels. An audio CD uses 16 bits which yields 65536 levels and extremely low hiss.
  3. Move the fader very quickly up and down repeatedly. Notice that the sampled stream no longer reflects the true motion of the fader. This is because the rate at which we are sampling is too low. This is called "under sampling" and results in an effect called "aliasing". Aliasing causes an unpleasant enharmonic distortion of high frequency sounds.
  4. Move the fader all the way to the top and bottom. Our "ADC" cannot handle the full range of the fader. Notice that the sampled numbers flatten out when the fader nears the ends. This is called "clipping". This can cause a buzzing distortion when one trys to record a signal that is too loud.