<< Chapter < Page Chapter >> Page >
Frequency modulation (FM) in the audio frequency range can create very rich spectra from only two sinusoidal oscillators, and the spectra can easily be made to evolve with time. The mathematics of FM synthesis is developed, and the spectral characteristics of the FM equation are discussed. Audio demonstrations as implemented by LabVIEW VIs illustrate the relationships between the three fundamental FM synthesis parameters (carrier frequency, modulation frequency, modulation index) and the synthesized spectra.
This module refers to LabVIEW, a software development environment that features a graphical programming language. Please see the LabVIEW QuickStart Guide module for tutorials and documentation that will help you:
•Apply LabVIEW to Audio Signal Processing
•Get started with LabVIEW
•Obtain a fully-functional evaluation edition of LabVIEW

Overview

Frequency modulation ( FM ) is most often associated with communications systems; for example, you can find all sorts of music stations on the FM band of your radio. In communicationssystems the baseband signal has a bandwidth similar to that of speech or music (anywhere from 8 kHz to 20 kHz), and the modulating frequency is several orders of magnitude higher; the FM radioband is 88 MHz to 108 MHz.

When applied to audio signals for music synthesis purposes, the modulating frequency is of the same order as the audio signals to be modulated. FM can create very rich spectra, andthe spectra can easily be made to evolve with time. The ability of FM to produce a wide variety of interesting spectra from only two sinusoidal oscillators makes FM a fascinating synthesis technique.

Brief history of fm synthesis

John Chowning was the first to systematically evaluate FM in the audio spectrum, and along with Stanford University, filed for a patent on the technique in 1975 (see U.S. Patent 4,018,121 at U.S. Patent and Trademark Office or at Google Patent Search ). The patent was issued in 1977, and Stanford University licensed the technology to Yamaha Corporation. Six years later in 1983, Yamaha introduced the revolutionary DX7 synthesizer ( ), the first commercially successful instrument based on FM synthesis. The DX7 was also a milestone by introducing two other new technologies: digitalsynthesis and MIDI (Musical Instrument Digital Interface). The "FM sound" defines much of the pop music styles of the 1980s.

Yamaha DX7 synthesizer, the first commercially successful instrument to offer FM synthesis, digital synthesis, and MIDI compatibility. The instrument pictured here is packaged in a road case.Photographer: schoschie ( (External Link) ). Copyright holder has granted permission to display this image under the Creative Commons Attribution-ShareAlike license .

Fm equation

The basic FM equation is presented in :

y ( t ) = A sin ( 2 π f c t + I sin ( 2 π f m t ) ) ,

where the parameters are defined as follows:

  • f c = carrier frequency (Hz)
  • f m = modulation frequency (Hz)
  • I = modulation index

The screencast video continues the discussion by explaining the significance of each part of , and demonstrates in a qualitative fashion how the different parameters of the equation influence the spectrum of the audio signal.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Musical signal processing with labview -- modulation synthesis. OpenStax CNX. Nov 07, 2007 Download for free at http://cnx.org/content/col10483/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Musical signal processing with labview -- modulation synthesis' conversation and receive update notifications?

Ask