[AudioI] stereo sound card on RPi4

[Bill Kunkle]

Matt,

Thank you for your reply.

Yes, the stereo sound card and SD card with the OS were transferred from
the RPi3 to the RPi4.  The RPi3 uses a 2.5 amp power supply.  The RPi4 uses
a 3.0 amp power supply.  So the power supplies were different for each
computer.

The bcm2835 has been blacklisted.  The stereo sound card is the only one
that shows up using aplay -l

It appears that most of the noise is being created by the RPi4 power
supply.  I used a micro USB to USB-C converter to connect the RPi3 power
supply to the RPi4 and here is the result - see image.

The tests were done using WiFi.  At some point I will do another test with
the RPi4 connected to ethernet to rule out any noise from the WiFi on the
board.

Thanks for your help.

[image: RPi4 stereo with RPi3 supply.JPG]

On Mon, Jan 17, 2022 at 1:35 PM Matt Flax <matt at audioinjector.net> wrote:

> This is a nice puzzle !
>
> OK, I would imagine that the power supply would effect very low frequency
> noise and a bad power supply would possibly have spurious tonal spikes
> through the noise floor. You confirmed that the power supply didn't change
> the effects below.
>
> Just restating what you said, the same sound card is being used, the same
> power supply and all other equipment remains the same. The only change is
> the Pi 3 becomes a Pi 4. The same operating system is running on both.
>
> Please double check that the alsa mixer has no side paths for audio to sum
> together and that you are receiving audio from one source only in the codec
> mixing fabric.
>
> There are two possibilities for these signal effects Either noise floor
> issues or signal corruption.
>
> Is there a way to measure the noise floor of this system ? To do a sound
> card alone measurement,. you will need to plug the output to the input of
> the sound card - this will confirm that there is no noise floor problem.
>
> How can we test for signal corruption ? Is it possible that the Pi4 is
> generating these spurious signals ?
>
> Matt
>
>
> On 17/1/22 1:50 pm, Bill Kunkle via People wrote:
>
> I collect data from VLF radio stations for the Stanford SOLAR Center for
> detection of Sudden Ionospheric Disturbances (SID).
> I've been using an RPi3 with the audioinjector zero sound card feeding the
> signal into the mic input.
> I recently purchased the audioinjector stereo card and I am feeding the
> signal into the line in input.
> With the stereo card on the RPi3 I can get very good signals above the
> noise floor as shown below:
> [image: RPi3_stereo.JPG]
> I transferred the stereo card and the SD card to a RPi4 and I get this:
> [image: RPi4_stereo.JPG]
> I've tried two RPi4's and two different power supplies (both from Canakit).
> The RPi3 is working very well with the stereo card but I do not understand
> why the RPi4 does not work as it should.
>
> Any thoughts would be appreciated.
>
> Bill
>
>
> --
> Checkout the community email list :https://lists.audioinjector.net/mailman/listinfo/people
>
>
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