Frequently Asked Questions

Q: What can I use Zelscope for?
A: Zelscope is a low-frequency oscilloscope and spectrum analyzer software. We believe it can be useful in tuning music instruments, adjusting audio circuits, or doing physics experiments. Acoustics is the most evident area; Zelscope also allows for an easy measurement of short time intervals in mechanics experiments. Zelscope has proven useful in debugging music and sound processing software.

Q: Where can I get the probes? Can I connect my sound card directly to my circuit?
A: It is dangerous to connect the sound card to anything other than standard audio equipment. The authors and distributors of Zelscope are not responsible for any injury and/or damage to your hadrware and/or data that can potentially occur. The typical input voltage should be about 1 volt AC at the line-in jack of the sound card, so a voltage divider or a buffer amplifier is highly recommended. A schematic is available here (that site is not affiliated with Zelscope, and we take no responsibility for its contents). A kit for a similar buffer circuit can be purchased from Jaycar Electronics, Cat. No. KA1811.

Q: I start Zelscope but all I see is a level green line, no signal. What's wrong?
A: Check the sound mixer settings, so that the correct recording source is selected. The mixer is normally found under Control panel, Sounds and Audio, Audio - Sound recording.

Q: How do I calibrate Zelscope to read real Volts?
1) make sure that the vertical offset for CH1 is zero (up-down slider in the middle position);
2) apply a signal with a known amplitude;
3) using V/DIV buttons and slider, adjust gain so the visible amplitude of CH1 is 2 divisions or higher;
4) click CAL button, answer OK to the message box;
5) click on the trace at the point of known voltage.
6) type the reference voltage in the dialog box, click OK. The vertical scale may abruptly change, as the V/DIV setting will be now a real one.
Calibration can be saved using Settings - Save settings menu.

Q: Can Zelscope display DC voltage?
A: No. All known sound cards contain a capacitor which provides AC coupling and prevents DC from reaching the card's analog to digital converter. Low-frequency oscillations (below 15-20Hz) usually get through, but may be distorted.

Q: Frequency readout is obviously wrong (64.6Hz instead of 60Hz, 430.6Hz instead of 440Hz, etc). What to do?
A: The FPEAK frequency readout is obtained from a Fourier transform (FFT) of the signal. This frequency is an integer multiple of the FFT resolution, which is 21.53Hz with default settings, and is inversely proportional to the buffer length. To improve the FFT resolution, increase buffer length using Settings - ADC and buffers menu. The maximum allowed buffer length is 800 ms, giving a 1.35Hz frequency resolution. For clean periodic signals you can also get an accurate frequency measurement in the time domain, by clicking left and right buttons on the successive crests of the wave. The frequency is then displayed in the 1/dT box in the Zelscope Cursors window.
Deviations of the actual sampling frequency from its nominal value vary for different sound cards, but are on the order of 1:10,000.

Q: Is Zelscope available for Linux or Mac?
A: No. Other similar tools are available for these systems, try searching for xoscope or Amadeus.

Q: I have a question which is not answered here
A: Your questions, suggestions, and bug reports are always welcome at

Copyright © 2001-2006 K.Zeldovich, N.Shusharina