Rockbox Technical Forums

Support and General Use => Recording => Topic started by: ljones on June 25, 2013, 01:06:31 PM

Title: Interference on sansa clip plus recording
Post by: ljones on June 25, 2013, 01:06:31 PM
Hello all :) !

Just wondering if anyone else out there has had this problem before and if there's a fix (or if it's just a general problem with the sansa music players). The sansa device in question is a sansa clip plus and I've tried both the dev build (46ea8bf) and official build of rockbox on this device. However I always run into the same problem -- interference on FM recording.

Here (http://slothpuck.no-ip.org/tmp/R_FM_130625-185243.wv) is a link (wavpack format) recorded on the sansa clip plus itself running rockbox. Note the interference hits about 15 seconds in, then 32 seconds in. Dosen't seem to be any locally generated interference external to the device as it happens in different places. Tried the sansa at work and at home and same problem x.x .

The interference dosen't occur if I just "listen" to the FM radio, only on record.

My guess (not sure!) is that it's being caused when the device writes data. Though I'm not sure. Does anyone know if I can stop this interference at all?

ljones
Title: Re: Interference on sansa clip plus recording
Post by: saratoga on June 25, 2013, 01:13:04 PM
I doubt anything can be done about noise during writes. 
Title: Re: Interference on sansa clip plus recording
Post by: jhMikeS on July 11, 2013, 04:28:09 AM
I doubt anything can be done about noise during writes.

We could limit the maximum size of the recording buffer to break up writing noise to small bursts instead of long ones.  :-X
Title: Re: Interference on sansa clip plus recording
Post by: ljones on September 16, 2015, 06:56:13 PM
I apologise for reviving such an old thread, but I nethertheless I'd try to follow this one up. I tried my old sansa clip + once again but this time I decided (never tried it before!) to record from the FM radio by using the inbuilt firmware.

You can download a very short mp3 here (http://slothpuck.no-ip.org/tmp/sansa_test_file.mp3) . That was just recorded off the devices' built in FM radio on the original (i.e. not rockbox) firmware. All I can say is .... ouch. What went wrong I wonder? Although rockbox seems to generate interference on writing on my device it isn't *that* bad - that is, rockbox works significantly better.

But given all that interference on that recording from the normal default built-in firmware surely that must mean I just have a bad player? Surely sansa didn't sell these devices with such a massive defect?

I should point out that interference isn't coming from some other device or place btw.

Does anyone else have a sansa clip plus to try at all?

thanks

ljones
Title: Re: Interference on sansa clip plus recording
Post by: ljones on September 25, 2015, 10:46:46 AM
Still need to do some more investigation on this one btw. I also think I'm slightly mixed up on my rockbox versions (though no matter which version I try the end result was the same!). According to rockbox-info.txt, I'm using version "1cada1f-150911".

One thing I've noticed though I'm not sure if it is just a fluke or not is that it seems like the interference might be mitigated somewhat by what sort of headphones you attach to the device. This really shouldn't matter but maybe it's some sort of weird impedence mismatch/problem or prehaps some headphones cause the device to "pick itself up" more than others - I have no idea.

Here (http://slothpuck.no-ip.org/rockbox/sansa_clip_plus/IMG_20150925_162443.jpg) are 3 headphones that I used with my clip plus while recording the FM radio.

Top left is a Shure SRH440 (expensive!) headphones. Top right those are Sennheister EH1430 headphones (from the late 90s, and with a very long cable). At the bottom, a cheapo "sony walkman" headphones, model MDR-027.

I tried recording the FM radio with all three. I'm still really investigating here, but for some reason if I used the shure headphones I got the exact same problem above. The sennheister and cheapo sony headphones were *much* quieter - in fact I could hardly hear the noise.

I still have to try out different sample rates and other rockbox versions.

ljones