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Sansa - prolonged electrical noise when loading tracks

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vitess:
The Sansa e200 has a known issue which results in electrical noise from the headphone-out when the unit reads from flash. On higher impedence headphones (e.g. the stock Sandisk earbuds, my 80 ohm Beyerdynamic DT250-80) it's difficult to hear, but with lower impedence headphones, such as my 16 ohm Sennheiser CX300s, it is clearly audible.

The behaviour of the stock Sandisk firmware trivialises this issue because it only reads from flash for about two seconds at the beginning of each track. Rockbox, however, seems to buffer the current track and each subsequent track up to available RAM. This makes sense for hard disk players, but on this flash player it's unfortunately exposing a nasty little hardware flaw. The result is almost 15 seconds of sustained electrical noise at the beginning of a track that hasn't been pre-buffered, which is difficult to ignore with tracks that start quietly.

Has anyone else experienced this issue with Rockbox and their e200? Unfortunately I can't provide a sample of the noise as I'm on the road at the moment, but I'll post a followup when I get the chance.

When I asked in the IRC channel I was told there's no way to change the buffering behaviour. I did however find a rather inelegant workaround of editing config.cfg to increase "max files in dir" to 250000 (I hope this flexibility is a feature and not a bug that gets fixed!). Each increase of 10,000 eats approximately 0.9 MB of buffer, and reducing the buffer from the initial 30 MB to around 7.5 MB results in buffering behaviour closer to the Sandisk firmware. I haven't used Rockbox for long enough to tell whether there are any negative side-effects (e.g. will games still have enough free RAM to run?).

P.S. Just a word of thanks to the Rockbox developers for creating firmware that is far superior to the manufacturers' concoctions. I'll definitely be donating a few dollars to the project as soon as the financial pain of my e280 purchase wears off :-)

Llorean:
The plugin buffer (used by games) is pre-allocated, you can't eat it up by increasing how much memory is used, because that memory is stolen only from the audio buffer.

Another option would be to compile a build with a significantly larger plugin buffer. This would not only reduce the noise duration (at increased frequency of the noise, much as yours does), but would allow much, much larger images to be loaded with the jpeg viewer without stopping music playback.

Though of course, still not a good option for the HD players.

Vagabund:
Hi vitess,

i have with my Sansa e270 the same problem. But i can hear also the noise while changing in the menu with the scroll wheel. But the noticeable noise is the "tic-tic-tic" electrical noise always if i play a song or in the pause. This is for me the absolut K.O. criterion for Rockbox, sadly. I like Rockbox, but the primary job for the player is to play music in good sound quality. I hope for a solution.

My inear from UltimateEars the superfi 5 pro has 21 Ohms.

Regards
Michael

mschneider:
Llorean,

About compiling for a larger buffer:
Would this also allow for larger images to be loaded in the wps? I know you said something about it in another thread and that doing so would eat away at audio buffer memory but if i were to compile for a larger image buffer where would it be in the source to modify?

vitess:
Michael, I get the electrical noise during menus etc. when the unit is reading from flash, but reducing the buffer in the roundabout way I described has greatly reduced its annoyance during songs. I'm not sure about the "tic-tic-tic" you mention. Are you saying your unit emits such a noise constantly while a track is paused?

I never got around to providing the promised sample of the electical noise - sorry about that. Probably won't bother with that unless someone requests it.

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