I had posted in another discussion here (Frequency response not working in mirror mode…) about using an expochip .wav file to measure the frequency response of a portable media player. I purchased another player which has dual ES9219 DAC chips. I tried with -10dBV and 0dBV 20-20khz QA403 generated expochirp /wav files As I done very little DAC frequency response testing, I was wondering if this response looks reasonable- mainly the small noise ripple in most of the waveform. I have tried both the line out and headphone settings on the player, and the results are pretty much the same once the headphone level is adjusted for appropriate output. There are some digital output filters that can be selected- I tried one and it made no difference. Are there settings in the QA40x that I should have set when doing this? Thanks for your time.
Here is the response with a 0dBV expochirp .wav played back with the lineout selected (the expochirp level is set real low just in case it comes on during the test ?):
Is this a triggered aquisition (from playback of a modified chirp file saved) or is it PC mirroring to the D/A in player?
Is there an issue with latency?
And are your FR settings greyed out like mine? (phase/harmonic display etc)
Thanks so much @restorer-john for trying to help me with this. It is a triggered acquisition from playback of a saved chirp .wav file that the player (HIFI Walker H20 Pro) is playing back. My amplitude is lower and the end frequency is double yours- I think I started out with 20khz:
The chirp file name is: Chirp_Bd32f_Fs48_Le64k_Pb2k_Am0.0dBFS. I do have a -10dBV " Fs96" chirp file and if I increase the sampling rate to 192k with a 128kFFT, I do not see the noise (10hz-30Khz range), but the lower frequency response is not as good,but probably good enough…?
I’ll try a few of my own here with the same settings and post back to the thread. Cheers.
I appreciate it, @restorer-john. It appears to have a better frequency response than my older DAP, though they both get that noise at the high end which I am thinking has to do more with the settings used to create the chirp as well as the sample rate and FFT. The trigger level of -25dbv seems to work most of the time. The trick I learned to get a good capture, was to set the chirp track to repeat continuously, pause it, and then move it to the beginning, and then press START on the QA40x and wait about 3 seconds before pressing PLAY on the DAP. In case you were interested, here is it’s THD/SNR measured with it set for Line out. THe 1khz tone .wav file used was generated by Audacity and very clean:
Hey VAR. I dug out a really old (2007) iriverX20 (2GB!). It still works after being in a drawer for years. Headphone out only (variable) and it seems to handle 44.1k or 48k files at 16 bit- not 32bit obviously.
Took my CBS-CD1 test disc, opened up Audacity as a 48k project, and imported the standard 997Hz 0dBFS dithered test track.Exported as signed PCM (16/48), put on the X20 and played it. This is the result at a medium high headphone level before distortion sets in, but it’s pretty good right up to full volume.
This was also at 42dBV, (forgot to turn off the attenuator):
Then exported the chirp at 48kHz, 32kFFT to a file. Imported that into a 48kHz Audacity project file and then exported as signed PCM, 16bit to play on the X20. (remember the files from the QA show up as 32 bit float)
This is the result connected as pictured below, to the QA’s L/R SE inputs.
Various input ranges tested:
I got a fuzzy one like yours, but it never repeated:
My settings are:
-25dBV for the trigger.
48kHz FS for the file and the QA FS
32k FFT size
~180mV for the 1kHz 0dBFS out of the headphone jack
The chirp was -20dBV default for the export IIRC?
Are you 100% sure the FFT sizes for the export and the analysis are the same and the sample rate for the exported chirp and sample rate you set for ananlysis? Perhaps you DAP needs a load on it? Some may not play well into a 100k impedance?
I can do some more with a greater zoom on the Y axis?
Edit: This is zoomed in to +/-1dB for the capture. I reckon that’s pretty good.
Hope that helps.
Wow- that is a lot of data- I appreciated it and it looks like your IRiver player is doing pretty good still. On some of my plots (not shown) I also could get that low frequency ripple you had on some of yours. I don’t think that it makes any difference for chirp measurements, but I used the Hann window and you the Flat top wind. Your +12dbv and +18dbv plots look very flat per the scale, at least. Both of my DAPS have line out settings, which as best I can tell just fixes the gain to the highest output level for the LineOut setting- If I can I will load it down with a load I have for preamps- ~48k and try that, as well as try to duplicate the settings you used- I never tried -20dBV export level. All your effort is appreciated, particularly with your ASR commentary about the switcher you built in college going on 
My mistake, it was -10dBFS - pretty sure the default setting? It just worked, so I left it alone.
I should have some time to play around with this some more today and will use those settings to create the chirp as well as match your playback settings and see what happens… @restorer-john Okay, it is later in the day and here is what I found out. Terminating the output of the DAP into a 47k load in parallel with the QA402 had no effect on the FR (the DAP was set for line out). My results were fairly consistent, but one would want to take at least three measurements to make sure it triggered correctly to give similar results- one time I got response with no noise, but could not repeat it. I tried both -10dBV and 0dBV 48ksampling and 64K FFTs for the chirp .wav files and both were consistent with having little noise on them, which is pretty small IMHO:
about 0.25dB. The Right channel has a bit less. That one I tried with with a 96k sampling rate and 64k FFT chirp .wav, but there was not really much change. The best overall response I got was this:
with a 48k sampling rate and a 64k FFT and a 0dBV level. It looks like there is about 2.5dB gain for my DAP’s line out based on a 0dBFS Chirp waveform being used (similar results for the -10dbFS chirp playback) ?? Even with the noise the frequency response looks pretty good, say +/- .17dB worst case. Not sure why the Right channel is a bit better, but that was pretty consistent with all the measurements. I may try testing another device at some point. Oh, tried 3 of the DAP’s digital filters but did not see a change.