FS#11405 - Rockbox fm reception is bad compared to original firmware

Attached to Project: Rockbox
Opened by Koen de Kok (Kakoon) - Monday, 14 June 2010, 23:24 GMT
Last edited by Bertrik Sikken (bertrik) - Friday, 15 October 2010, 18:14 GMT
Task Type Bugs
Category FM Tuner
Status Closed
Assigned To No-one
Operating System Another
Severity Low
Priority Normal
Reported Version Release 3.6
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No


The rockbox fm radio tuner locks to mono very quickly compared to the official firmware on my sandisk sansa fuze 4gb. I have a strong fm transmitter about 500 meters from my house, and depending on the place in my house, the rockbox tuner falls back to mono at several places where the original firmware doesn't. I used to have a good stereo reception of this station on the way to my work (10 km away), now with rockbox, signal is lost very often.
This task depends upon

Closed by  Bertrik Sikken (bertrik)
Friday, 15 October 2010, 18:14 GMT
Reason for closing:  Fixed
Additional comments about closing:  Should be fixed in SVN r28284.
Comment by Bertrik Sikken (bertrik) - Tuesday, 15 June 2010, 08:37 GMT
This is indeed something we can have control over. The fm chip has a setting that determines at which signal level the chip starts making the signal gradually more "wide" (stereo). I assume we currently use the default. As far as I can see in the si4702 datasheet, the stereo level switchover point can be adjusted either 6dB or 12dB lower (these are the BLNDADJ bits in the SYSCONFIG1 register).
Comment by Bertrik Sikken (bertrik) - Monday, 21 June 2010, 21:54 GMT
Attached is a patch that lower the level at which stereo is enabled by 6 dB, please try it.
Comment by Koen de Kok (Kakoon) - Tuesday, 22 June 2010, 18:09 GMT
Hey Bertrik, first, thumbs up for the quick reply!

I compiled rockbox with your source patch. Hope I did it right... I deleted the .rockbox folder to make sure no old files were there, and then unzipped the created to the player (because only copying the to the root gave a 'file not found'?). After unzipping it worked though.

I did a test with a small fm transmitter (Belkin Tunecast 3). Broadcasted some music on it, with the right channel muted. The original sansa firmware can play full stereo (absolute silence on right) within a range of about 5 meters, but the rockbox firmware still only plays stereo when I hold the mp3 player really close to the transmitter, nearly touching it.

So I'm not sure if reception improved, but it's still far from comparable to the original sansa fuze firmware. I will test more tomorrow on the way to my work.
Comment by Bertrik Sikken (bertrik) - Thursday, 01 July 2010, 20:08 GMT
Attached patch further lowers the signal level where stereo is enabled.
It's not clear to me whether it's a stereo level problem or a generic signal reception problem.