Low input sensitivity

Moderator: flatmax

robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Low input sensitivity

Post by robiwan » Wed Aug 30, 2017 9:36 pm

Hi Matt, I have a solution now which streams audio, but I notice that full output from a USB audio device couple to the input of the I2S card does not even remotely reach +0db peak level, more like -20 dB peak. Is there a way to set the PGA of the WM8731 for higher sensitivity ?

flatmax
Posts: 609
Joined: Sat Jul 23, 2016 11:39 pm

Re: Low input sensitivity

Post by flatmax » Wed Sep 06, 2017 8:07 am

Hi there,

Have you bumped the gain up in alsamixer ? Did that have any effect ?
Matt
Check out our audiophile quality crossovers : https://bit.ly/2kb1nzZ
Please review the Zero sound card on Amazon USA : https://www.amazon.com/dp/B075V1VNDD
---
Check out our new forum on github : https://github.com/Audio-Injector

robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Re: Low input sensitivity

Post by robiwan » Wed Sep 06, 2017 4:40 pm

Yup, I have everything set to max, still having this issue. I will try to do a measurement of the exact levels, analog and digital.

robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Re: Low input sensitivity

Post by robiwan » Mon Nov 20, 2017 12:22 am

Ok, I've done a loopback test where I playback (with aplay) a 0 dB fullscale WAV file, and the result is recorded with arecord. I would have expected that the result would be approx. 0 dB peak, but it is far from it. The result is at least 6 dB lower than fullscale. See attached files.

Could it be a driver issue ? I.e. that the PGAs of WM8731 aren't setup correctly ?

Regards
/Robert
Attachments
test.wav
Result of arecord
(187.54 KiB) Downloaded 282 times
playback.png
Playback settings
playback.png (21.33 KiB) Viewed 5297 times
capture.png
Capture settings
capture.png (17.94 KiB) Viewed 5297 times

robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Re: Low input sensitivity

Post by robiwan » Mon Nov 20, 2017 12:34 am

Furthermore, here is an Oscilloscope screenshot of the output of the soundcard. The datasheet states 1.0Vrms*(AVdd/3.3) and as the AVdd is 3.3V, the output should be peak +/- 1.4142V, which the scope screenshot verifies. So the problem is on the input side.
Attachments
SDS1202X-E1.png
Screenshot of output signal ~ 1.0Vrms
SDS1202X-E1.png (19.09 KiB) Viewed 5296 times

moggyd
Posts: 22
Joined: Wed Jul 05, 2017 5:09 pm

Re: Low input sensitivity

Post by moggyd » Mon Nov 20, 2017 8:51 am


robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Re: Low input sensitivity

Post by robiwan » Mon Nov 20, 2017 9:12 am

Ok, I'm not sure what this means. It is ambiguous. Is there a 6 dB attenuation on the input or not ? But not on the zero card ? The boost mentioned seems to imply soft volume, which means digital boost of 6 dB. That is unacceptable. The datasheet of WM8731 says 1Vrms*AVdd/3.3 at 0 dB FS. That is what I am after.

moggyd
Posts: 22
Joined: Wed Jul 05, 2017 5:09 pm

Re: Low input sensitivity

Post by moggyd » Mon Nov 20, 2017 9:23 am

There is a 6dB limit on input of the full size card but not the zero version. I have no idea why.
Using softvol is far from ideal for me but does make the card usable

flatmax
Posts: 609
Joined: Sat Jul 23, 2016 11:39 pm

Re: Low input sensitivity

Post by flatmax » Fri Nov 24, 2017 8:13 am

The full sized card has a resistor divider on the input side. This causes the 6 dB attenuation.
To bypass this attenuation, please short resistors R6 and R7.

As mentioned, the zero sized card doesn't have this attenuation on the input.

thanks
Matt
Check out our audiophile quality crossovers : https://bit.ly/2kb1nzZ
Please review the Zero sound card on Amazon USA : https://www.amazon.com/dp/B075V1VNDD
---
Check out our new forum on github : https://github.com/Audio-Injector

robiwan
Posts: 59
Joined: Wed Jul 05, 2017 1:18 am

Re: Low input sensitivity

Post by robiwan » Fri Nov 24, 2017 7:18 pm

Yay! I suspected something of the sort :) Thanks!

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