lcd noise on sansa

[rp]

Hi!

i just tested recording on my sansa and noticed a very annoying high frequency noice when the lcd is on (or maybe just the backlight??).

have anyone a idea about it?

isn't there a same issue with playback and buffering of files?

EDIT:
rockbox-version: r13583 with sd-card patch applied

[Vortex]

noticed a very annoying high frequency noice when the lcd is on

The same thing happens in the Original Firmware so I don't think there is a way the Rockbox developers can fix this.

There should be added a new Option "Backlight while recording" the the LCD Settings menu.

[rp]

shame on me!

didn't check if the OF has this behavior too, and you are true, just checked that.

so it's no rockbox bug, sorry

[Chronon]

It would be slick if you could add this signal back in with a Pi phase shift to cancel it out (e.g. noise cancellation).

[Vortex]

I think it would be easier to simply turn off the backlight while recording, or rather set the backlight timeout to 1s or something like that. I know that this would be a workaround and not a fix but when dealing with hardware limitations a workaround might be the only solution.

[Chronon]

Vortex, that sounds like a decent workaround and much simpler than trying to implement synchronous detection and mixing!

[quincy]

i think everything does that. i notice even on my pc there are quiet sounds whenever i use headphones and just move around windows and such
of course, that has nothing to do with an lcd screen, but whatever. i think it probably has something to do with magnetic fields and everything being packed together into such a small space

[Chronon]

Sure.  Any circuit of reasonable complexity will exhibit both inductive and capacitive coupling.  

The issue here is identifying the dominant sources of noise and quelling them if possible.