I'm using a PicoScope 2000 to perform some simple audio testing in the vocal range. Channels A and B of the PS are plugged into the headphone jack of my output device. The PS2000 generates a signal sweep in the audio range which is played through speakers, whose output is recorded through a microphone/amplifier and analyzed with the PicoScope.
In analyzing what appeared to be very high levels of Total Harmonic Distortion (presumably from the speakers themselves) I decided to get a baseline THD of the PicoScope itself to use as a reference point and was very surprised to see very high THD with a simple sine wave at 1kHz. Attachment 1 is a screenshot of the spectrum view with associated vitals.
Attachment 2 highlights the spectrum of interest for data collected during a full sweep from 300Hz to 3kHz.
All I did was plug the PS2000 output into the PS2000 Ch.A input, in effect using the PS2000 to analyze it's own signal. So....
What is the source of this distortion? Is real, or an artifact?
Might it influence the THD of my system of interest?
How do separate it from that THD generated by my audio system to be tested?
Would it be possible to send in the PicoScope 6 data files corresponding to the screenshots so that we can check your settings please? You can post them here or e-mail them to support@picotech.com
Thanks for the YouTube seminar; it was very useful! I'm really surprised, however, that the THD of the 2205 (as I measured it) is almost three times worse than the 4206.....if that's even the correct way of interpreting my result.
I guess I should expect that the 12bit resolution of my inexpensive 2204 unit is no match for the 16bit resolution of the far more expensive 4206 unit illustrated in your example, but I'm not clear where the distortion "lives" on my unit when I measure the self-produced signal of my picoscope. Does the signal generator produce a "distorted" signal to begin with? and does the 2204 simply add to that distortion?
Just to clarify, the PicoScope 2204A is an 8-bit resolution device. The 12-bit resolution can be obtained via the PicoScope 6 Resolution Enhancement feature.
It is likely to be a combination of the PicoScope 2204A signal generator and the inputs.
Comparing the specfications for harmonic distortion:
PicoScope 2204A: < -50 dB at 100 kHz, full–scale input