BorisS
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Camera induces heavy noise to USB microphone

Tue Jan 28, 2014 9:10 pm

Once the camera is activated it induces heavy noise into a microphone that is connected to an USB sound card which itself is connected to the same Pi.

Has anyone some experience how this can be stopped/reduced? E.g. something like an USB extension cable with ferrite ...?

jamesh
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Re: Camera induces heavy noise to USB microphone

Tue Jan 28, 2014 9:55 pm

What sort of camera is it?
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redhawk
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Re: Camera induces heavy noise to USB microphone

Tue Jan 28, 2014 9:59 pm

What kind of noise can you hear, i.e. high pitched whistling or a low frequency buzzing sound??

Richard S.

BorisS
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 8:10 am

The camera is a PiNoIR (connected with with default flex cable, pointing away from usb ports as far as it is possible).

Difficult to judge the noise. Approximately Gaussian in the low and medium frequency range. It is always present in video mode and bursty in raspistill timelapse mode.

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Burngate
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 11:33 am

Quite possibly power-related. The camera takes a fair bit of current, so the 5v may be dipping or getting ripple.
Given that audio is quite low level, the mic and USB card needs a decent supply. If it doesn't have a well-regulated power circuit built in, anything on the 5v rail will get into the analogue circuitry.
So a powered hub is a necessity. Ferrite beads can help, but keeping the Pi and hub supplies separate is better.

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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 11:52 am

Could be transmitted noise from the ribbon cable, but that is in the Mhz range so maybe a bit high for audible noise. Wrap it in tin foil as a check?
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 6:11 pm

BorisS wrote:Once the camera is activated it induces heavy noise into a microphone that is connected to an USB sound card which itself is connected to the same Pi.
.....
All 7 usb ports occupied on the hub & 1 on a RPi.

USB "card":

[email protected] ~ $ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: Set [C-Media USB Headphone Set], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0

Just a condenser mic':

[email protected] ~ $ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: Snowball [Blue Snowball], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
[email protected] ~ $ arecord -Dplughw:0,0 - | aplay -

These tests were made whilst running:

[email protected] ~ $ raspivid -t 0

& no difference in noise level with or without the camera running.

My M-Audio Fastrack was similar, apart from sending the Terminal berserk, but I think that is owing to updating RPi firmware (3.10.28+) today, as my tuner has stopped working too (reported).

Can you post a noise sample as an attachment, along with firmware & kernel version?

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redhawk
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 6:19 pm

Just out of curiosity are you using Composite video, HDMI or neither??

Richard S.

BorisS
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 8:06 pm

Update:

- Shielding cable with a tin didn't change things noticeably (maybe shielding was not properly grounded, but I also guess transients on power rail are more significant).

- A powered hub solved the problem! Thanks for this proposal. It's only a pity that an extra wall wart, usb hub, sound card, and cabling is required to attach a tiny mic.

Ok, probably I didn't recall noise correctly (it's not so Gaussian). Unfortunately, this forum does not allow me to upload the .wav samples.

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redhawk
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 8:24 pm

The problem with these tiny mics (aka condenser or electret) they require something called "Phantom Power" which usually involves a small resistor connected to the +Vcc supply rail of the USB device.
This wouldn't had been a problem if the power supply was nice and smooth but since the camera was causing ripples it was inadvertently getting injected into the microphone input.
A well designed amplifier would compensative using a differential or long tailed pair amplifier stage but that just complicates the design. :)

Just out of curiosity what is the current rating of your power supply??

Richard S.

BorisS
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Re: Camera induces heavy noise to USB microphone

Wed Jan 29, 2014 8:32 pm

I do use the 2.1A power supply from Farnells RasPi shop and my Pi runs headless. And yes it's an electret mic with three inputs (signal and power are separated).

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