This audio oscillator project presents an advanced DSP simulation flow graph.  This DSP generates an audio tone that is variable in frequency and audio amplitude.  Additional features include multi-rate sampling and an FFT panadapter display.  The advanced features illustrated in this project can be applied broadly to other GNU Radio DSP flow graphs as needed.

This flowgraph differs from the Simple Audio Oscillator Project Simple Audio Oscillator in that the flowgraph includes a change in the samp_rate seen in the Variable block, and three additional DSP blocks: two Rational Resampler blocks and a WX GUI FFT Sink.  The Rational Resampler blocks adjust the samp_rate of 5,120,000 samples per second to reduced sample rates compatible with optimal operation of the WX GUI FFT and Audio Sinks.  Note the samp_rate was decimated by factors in each Rational Resampler block to achieve the desired samp_rate for that particular Sink.

Advanced Audio Oscillator Flowgraph

Once executed the operating GUI appears on the screen.  Note the FFT panadapter display with the default 250 Hz source frequency nicely displayed.  Varying the Audio Tone slider will move the signal display within the FFT display.  The Audio Amplitude slider will vary the audio volume.  Note that with the increased samp_rate the controls provide much more smooth control with reduced latency.

Advanced Audio Oscillator Operating GUI

The procedure for downloading a .grc file is here: Downloading .grc files  The .grc file with an annotated flowgraph for this project is available here: Advanced Audio Oscillator