3.1 [ mini-project ] compose a piece of music using analog synthesizer  (Page 28/2)

Objective

This project will give you the opportunity to begin designing sounds in LabVIEW. You will create two subVIs: one to implement an ADSR-style envelope generator and the other to create a multi-voice sound source. You will then create a top-level application VI to render a simple musical composition as an audio file.

Prerequisite modules

If you have not done so already, please study the prerequisite module Analog Synthesis Modules . If you are relatively new to LabVIEW, consider taking the course LabVIEW Techniques for Audio Signal Processing , which provides the foundation you need to complete this mini-project activity, including working with arrays, creating subVIs, playing an array to the soundcard, and saving an array as a .wav sound file.

Deliverables

• All LabVIEW code that you develop (block diagrams and front panels)
• All generated sounds in .wav format
• Any plots or diagrams requested
• Summary write-up of your results

Part 1: adsr envelope

Create the subVI ADSR.vi to generate the ADSR-style envelope specified in ; recall that ADSR stands for "Attack Decay Sustain Release."

The envelope shape is defined over a normalized time interval of 0 to 1; the envelope stretches or compresses to match the actual duration requested. The three time intervals are likewise expressed in normalized units, so an attack duration (tA) of 0.2 indicates that the attack time is 20% of the entire envelope duration. The envelope values range from 0 dB (full sound intensity) to -40 dB (close to silence). Once you have defined the envelope shape in terms of straight-line segments, you can create the envelope amplitude waveform by undoing the decibels operation; recall that an amplitude "A" expressed in dB is 20 log10(A).

The subVI requires the following controls as input parameters (units specified in brackets):

• duration [s] - total duration of envelope
• fs [Hz] - system-wide sampling frequency
• t values - three-value array containing attack (A) interval, decay (D) interval, and release (R) interval. All three values are in the range 0 to 1, so the intervals are to be treated as fractions of the total duration of the envelope. For example, A=0.3 indicates the attack interval is 30% of the envelope's duration.
• e values - two-value array containing the envelope value at the beginning of the sustain interval (eS in the diagram above) and the envelope value at the beginning of the release interval (eR).