Free to try Sound Card Oscilloscope, Spectrum Analyzer and Signal Generator

[TestGuru]

Free to download and try.

website: http://www.virtins.com
PC version: http://www.virtins.com/SCMISetup.exe
Pocket PC version: http://www.virtins.com/PocketINSSetup.exe

Virtins MultiInstrument consists of a sound card dual trace oscilloscope, a real time spectrum analyzer, and a signal generator and can run them concurrently. It features a specially designed data acquisition approach, which is able to monitor the input signal continuously without missing any trigger event before a frame of data is collected. It has a very fast screen refresh rate. It supports sophisticated triggering method including pre-trigger and post-trigger. A comprehensive range of functions are provided, including waveform addition and subtraction, Lissajous Pattern, transient signal recording, voltmeter, RMS amplitude spectrum, relative amplitude spectrum, octave analysis(1/1,1/3,1/6,1/12,1/24),THD, THD+N, SNR, SINAD, peak hold, phase spectrum, auto correlation, cross correlation, function generation, multitone generation, arbitrary waveform generation, white noise and pink noise generation and sweep signal generation. It Supports 8, 16, 24 bits and multilingual user interface, including English, French, German, Italian, Spanish, Portuguess, Simplified Chinese, Traditional Chinese, Japanese, and Korean.

[indulis]

The problem here is bandwidth... it's only as good a your sound card, and how high beyond 20KHz does it go.

[TestGuru]

Hi, Zeppelin,

Theoretically, there is no error in the output frequency as long as it is lower than the Nyquist frequency (i.e. half of the sampling frequency).

The actual frequency output accuracy will depend on how accurate the sound card's sampling rate is. Also, the software GUI only accepts integer frequencies to output.

A sound card based solution is cheap and good for test and measurement within audio frequency range.

Nowadays, a sound card can have a sampling rate of up to 192 kHz, a bandwidth of 10Hz~50kHz, and a bit depth of 24 bit. Moreover, it has two channels of A/D and two channels of D/A. So it can be used to do quite a lot things at very low cost, if you have a proper software.

[indulis]

Of course there is error, the question is how much and does it matter... what's the accuracy of the reference clock?

[TestGuru]

Hi, indulis

As indicated above, "The actual frequency output accuracy will depend on how accurate the sound card's sampling rate is"

Typically, the inaccuracy of sampling rate is in the order of 0.00x% for an ordinary sound card.

[indulis]

Yes, yes... at a minimum, you have to sample at least twice the frequency your trying to measure... blah, blah, blah. You could sample all day at 1000x the frequency, but unless you know where your starting from, it's worthless.

It's still all based on some reference!!! It can only multiply of divide some base clock... how acurate is that??

[TestGuru]

Hi, indulis,

The sampling rate accuracy is determined FULLY by sound card hardware.  A quartz on the sound card generates the reference clock. The accuracy of this reference is 0.00x% typically for an ordinary sound card. For example, a 0.003%'s inaccuracy in a sampling rate of 44100 Hz means an error of only 1.3Hz.

Unlike what you have described, the error in the sampling frequency is not accumulative, because we are dealing with frequency here, not the time of the day/month/year.
 
For example, if we use this sound card to generate a 1 KHz sinewave signal, the error in the output frequency would still remain at: 0.003%, i.e.  0.03Hz.

[TestGuru]

The amplitude accuracy depends on the quality of the sound card and, of course, the frequency of the signal under test.

There are quite a few parameters that can be used to characterize the analogue accuracy of a sound card, such as:

Frequency response, THD, THD+N, dynamic range, noise level,......

Some sound card manufacturers provide these paramteres in their manuals, but most do not.

There are also some websites who provide INDEPENDENT measurements of these parameters, for example:

[TestGuru]

Just an add-on to the above statement: "Nowadays, a sound card can have a sampling rate of up to 192 kHz, a bandwidth of 10Hz~50kHz, and a bit depth of 24 bit."

In fact, quite a lot sound cards support (input & output) frequencies down to 1 Hz or even below that.