I tried several different FFT/sample rate combos, as well as levels and with the Prepend noise on or off, but still get that ringing up to about 200hz. I am wondering if anyone has had similar ringing when testing such a device.It is about +/ 0.5dB, so not horrible. The frequency response of the preamp using the chirp is fine (via line in). I could generate a dozen or so low frequency tones using Audacity and play them back one at a time and do a manual stepped response measurement, but am trying to avoid that. I would appreciate your thoughts, Thanks.
Thanks for replying, and I did try averaging, typically 3, on one of the many attempts I made.
Follow Up- I decided to create tones (via REW) from 20hz-200hz every 10hz, and play them from my NAS drive into the QA, from the streamer’s line out again, and got this result, which kinda matches the chirp method decently:
I think what you’re seeing is a capacitor filling or decaying somewhere in the single chain. This generates a slowly decreasing DC offset and it’s not at all unusual when a device starts up.
As a test, you could try preceding the signal with a similarly-high-level sine wave at 1KHz or whatever with a short quiet time between and see if the DC offset then stays constant.
This is why Idle generation was so important with QA40xPlot. Now, when I do tests of external Windows sound devices (specifically not the QA40x) the first iteration is thrown away as garbage and the second iteration is captured.
If your streamer has USB input and can act as a DAC to windows->
@MarkZ Thanks for taking some time to reply to this and I did go over the link you provided. Unfortunately, this Streamer, surprisingly (?), does not have a usb input. When I plot it the “old school” way, loading a tone at time and putting down what I am reading on the QA into a spreadsheet (“Oh the Pain” ) I see a similar type behaviour, so I am thinking it is caused by something they did in the signal processing between the RF receiver/DAC…?
Could it be auto muting opening? If you look the plot you shared, see that little dip? Looks like a circuit got biased that hadn’t be biased. Stepped tones would for sure answer the question here. Chirps can be very susceptible to these types of events.
Is you prepend a lot fo noise at the beginning, does that change anything or reduce the wobble?
Thanks for the reply, Matt. I tried it both with & without the prepend noise being checked and it made no difference. The other plot was made with stepped tones- a lot of “work” since the have to be played manually from the NAS drive via the streamer’s app one at a time and then read on the QA403 & entered into excel. There are much worse things to do
@matt I haven’t listened to the chirps since the QA was hooked up, but will try listening later as the streamer is connected to a system now… Update- @matt I did hear the noise followed by the 1khz tone when playing back on the streamer, so I am guessing it is a “flaw” in it… Not a big one, IMHO.
) I see a similar type behaviour, so I am thinking it is caused by something they did in the signal processing between the RF receiver/DAC…?