Generate noisy sine waves with a sound card
A sound card, software, and an amplifier circuit is all you need.
José M Miguel, RF-Electronics Ltd, Barcelona, Spain; Edited by Martin Rowe and Fran Granville -- EDN, January 20, 2011
Testing audio-noise-reduction
circuits, PLLs (phase-locked
loops), and audio-frequency filters may
require a noisy sine wave, one that is
summed with white noise. Using a typical
computer sound card, free software,
and an external amplifier circuit, you
can create a noisy sine wave.
Free Generatosaur software from
Wavosaur turns
your sound card into a low-frequency
wave generator. It lets you independently
choose amplitude, frequency, and waveform
for the left and the right channels.
The Generatosaur’s user interface is a dialogue-box-style control panel (see Figure A). If you
select a sine wave for the left channel
and a white noise for the right channel,
you then need only to use an amplifier
to add the signals. Figure 1 shows the
complete circuit.The differential amplifier employs a National Semiconductor LM386 audio power amplifier with a supply voltage of 15V. The output of the LM386 has a self-centered quiescent voltage that is half the power-supply voltage and that requires a blocking capacitor, C3. Resistor R5 sets the output impedance to 50Ω.
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Figure B
shows a 450-Hz sine wave with
a 10-dB SNR (signal-to-noise
ratio). The root-mean-square
noise voltage of this signal is
0.5V measured
on an oscilloscope
and following the tangential
method. If you need to
hear the generated noisy signal,
connect a loudspeaker to
the output of IC LM386.
Talkback
-
Good idea.
If you eliminate the speaker, an opamp could be used with a cleaner signal. Of course, a little more circuitry is required.
Stan Hubler - 2011-1-2 17:28:32 PST -
My Daqarta software can generate up to 4 independent streams per stereo channel. Streams can be any standard waveform; or white, pink, Gaussian, or band-limited noise; or arbitrary waves from a file. Each stream can be independently modulated (burst, AM, FM, PM, and/or sweep). Streams can be mixed (such as to create the noisy sine waves in the article directly), or can be used as modulators for other streams. You can see the waveform, spectrum, or spectrogram in real-time. Extensive built-in help via right-click. All of this is free. (To monitor input lines requires a $29 license after the trial expires, or $99 for Pro features, but you don't need these to use the signal generator.)
Robert Masta - 2011-27-1 06:55:31 PST -
I have written and posted such a utility on my web site years ago: www.ko4bb.com/ToneGenerator/
Didier Juges - 2011-24-1 11:56:14 PST -
you can use Spectrum Lab, which allows mixing of up to 3 repetitive waveform sources and a noise source, and watch the DUT output spectrum on the analyzer window (also using the soundcard).
it's also freeware, and is a complete audio lab on a soundcard...
jed martin - 2011-23-1 15:54:37 PST -
That's a great little design Idea, thanks!
Waveosour is a great little editing program also.
Steve Hageman - 2011-20-1 11:58:19 PST
