My problem is different then the last topic. I can get the frequency response button to work in loop back. I hope BrotherTheo’s issue which posted first gets fixed soon…
I have been testing a high-quality external USB box using Mirror mode. I can get sine waves to the DAC and see the spectrum. I was also able to get the Amp Frequency Response to work. I watched as the tone moved up on the spectra as the script was running.
Are you saying I cannot Mirror an Expo Chirp and do a frequency response? Do I have to use the Amp Frequency Response in mirror mode as the only option? It is very slow compared to Expo Chirp.
If you want to use an expo chirp on an external sound source such as a DAC or your car, you can build an special expo chirp WAV, put it on an SD card and then do a triggered sweep. The mirrored tones are great when you need something quick. But there is often a lot of transcoding in Windows it can be frustrating getting something reliable from Windows.
I was thrilled to see the wiki on triggered sweeps, and decided to try it out. I have fiddled with several different FFTs and trigger settings, but it seems that I am not getting a long enough chirp (?) I exported a 0dbfs expochirp as well as a -10dbfs .wav file (following the example given), and put them a microSD card on my portable music player, so I could see how well it does, and these are about as good as I can get (0dbfs) and -8dbv trigger:
Hi @Var, just to make sure, the chirp you export is specific for a given sample rate and FFT size. So, pick both of those BEFORE you export the chirp.
The duration of the chirp will be tied to the FFT size. So, if you want a longer chirp, then increase the FFT size. Looking at the chirp you provided, it seems to have been processed correction. That is, the trigger isn’t present (which is correct), we see about 50 mS of silence before the chirp starts, and we see some silence after the chirp ends.
That the frequency response ends at 4 kHz is suspicious, though. In your time domain plot, zoom in on the last captured cycles are use cursors to determine the frequency of the last captured cycles.
Thanks for getting back with me on this, Matt- it will open up being able to look at more things if I can get it to work I will try again later today and maybe create another file. I will zoom in on the frequency once I get a new response up and report back.
I played with it some more and it seemed if I changed the trigger level to -40dbv, it worked fine and I was getting a -10dbv pretty much flat frequency response as I would expect (hope). I had been using higher trigger levels before, around -1dbv. When I tried it later, I was not able to get it to trigger and provide a reasonable waveform, or any waveform. The device I am playing these back on is a SURFANS F20 music player, and if I play an Audacity generated wav file, say 1khz at 0dbfs, and that is what I get, so it does work. Here is the expochirp wav file that I have been using- when imported into the QA402:
Hi @Var, note the dense trace right before the sweep starts. You shouldn’t be seeing that if you have your trigger set up correctly. You should start with trigger too high, and then lower it bit by bit until you get a trigger. And then, as the link I showed above shows, you want to make sure you have just the chirp.
If you are using a portable player, these DACs will often use a noise gate. Which means it might miss part of the initital burst and/or the chirp itself. So, you can enable noise generation and a low level to make sure the noise gate is opening on the player.
Thanks for the reply, Matt, as always. What I posted above was the actual waveform that the player was playing, as seen by importing it into the QA402 in this case. I did not have any different results when using the QA403. If I connect the output of the Dac to a stereo & listen to it, I hear some silence and then the 1k tone and the sweep, so I think the player is doing what it should. I only have one player to use unless I record it to a CD and try a CD player… I will fiddle around some more with the trigger levels…
You’ll have to convert the exported file from 32bit float 48kHz to 16/44.1 before you burn it to a CDR or the CD player will not play it. Some DVD players might?
I’ve been experimenting with CD players too and wanted to get @matt to chime in and confirm a bit on the triggered functions.
At 32kFFT/48ksps:
The preamble can be low level dither?
The trigger tone is 50mS (50 cycles) of 1kHz?
The gap before commencing acquisition is ~35mS? Does it have to be exactly that?
The expo chirp is 300mS@48ksps?
I wanted to be able to make my own files for burning to CDR, without having to SRC the 32/48 to 16/44.1 as we cannot do 44.1 natively in the QA403. (I figure that needs another XTAL TCXO?)
Hi @restorer-john, yes, you can for sure roll your own here. Take a look at the picture below from the link earlier and that will indicate the structure. Yes, you should replicate the timing between the end of B and the start of C.
The preample can be whatever you like, but it needs to be quite a bit below the trigger. I’ve had good luck with noise on every DAC I’ve tried. If you know the DAC IC in the DAC you are testing, then you can see how long it takes for the silence detection to kick in the chip spec. And then you could generate noise, and pause that noise for a bit before the trigger.
The trigger doesn’t need to be 1 kHz. But it needs to be about the amplitude of the chirp. I think you could take the WAV and transcode to 44.1 using desktop software no problem. Just make sure it’s a well-used tool and not something included with Windows.
I played around some more and seem to have better luck with the player’s headphone output more than the line output, which is what I had been using. The chirp is -10dbfs. Seems to work best with -15dbv to -10dbv trigger levels. Here is what I am seeing for the headphone jack (I wonder if the Freq response is really down 1dB at 20Hz?) :
I think the volume is set for 70%, but the line out has a greater output according to what I measured, but it has a lot more noise on the left channel as the frequency gets above 2kHz. I don’t have any schematics or block diagrams for the music player, but I am guessing that both the line amp and headphone amp are fed from what ever comes of the DAC/filters, so the low frequency response may be real. There may be something going on with my player as you said - may try it with a DAC…
When using Triggered Sweeps, is there any way to calibrate errors in the QA403 the way you do with Frequency Response with the Right Channel as a Reference?
Finally some good news and bad news. The good news is I was able get the expochirp to trigger the QA403 using my SMSL SU1 DAC 's USB input. Used a -25dbv trigger input and a 0dbfs chirp signal. I adjusted the Windows Media Player’s volume control to about 67% to get the DAC’s output to give 0dbv (not sure if that is normal). here are plots of the frequ response as well as the time plots:
This agrees very closely with ASR’s freq. response of the SU1, so life is good on that end. A whole new world of testing awaits me… THe Bad news is that my current portable media player is going to need to be replaced due to its freq response at the low end, will order the newer version of it with dual ESS9018 DAC chips and see how it compares…Thanks for the help!
I will try again later today and maybe create another file. I will zoom in on the frequency once I get a new response up and report back.
