Limiting on Sansa Clip+

[megal0maniac]

I was at a festival this weekend working at front of house and decided to record one of the bands with the built in mic on my sansa clip+ for interest sake.
Actual sound levels were around 97dB. In the recording (and on the level meter on the screen) the level would not exceed -13.4dBFS. It's as if the sound is being hard limited. Reducing the gain brought the recording level down as will as the brick wall, and increasing the gain just pushed the levels harder against the -13.4dB limit.
Why is this? Compression is disabled.

[saratoga]

What build?

[markanini]

I believe I'm seeing the same behavior on my Sansa Fuzev2 with latest build regardless of FM or mic source.

[megal0maniac]

How do I check build no? I updated about 2 days after the initial release of 3.9.1

[saratoga]

How do I check build no? I updated about 2 days after the initial release of 3.9.1

That means you're running a pretty old build.  Pretty sure I fixed this bug months ago.  Try updating and see if its still there.

[megal0maniac]

Shall do and post update here when I'm back in town.

[markanini]

Turns out I was using the current release as well. The current build does indeed make the levels go above -13dB as expected. However now I'm getting buzzing on my recordings: http://www.box.com/s/3z5bqarodqh41cuj1qmb

EDIT:
You'll also see the aliasing that I reported on in the general forum.

[megal0maniac]

Just installed the current build (31103-111201)
No more -13dB limit, but I'm getting the same buzzing sound as markanini

[Chronon]

Sounds like it might be this:
http://www.rockbox.org/tracker/task/11631

[megal0maniac]

Don't think so... My recording didn't clip with a 97dB source, just the recording level was low.
This comment talks about automatic gain control, which is what I think prevented clipping.

However, now it's a buzzing sound, not clearly visible in the waveform. Perhaps inaccuracies in the ADC?
From markanini's upload:


EDIT: If the buzzing was gone, the waveform wouldn't look any different.
Post Merge: December 03, 2011, 05:38:03 AMMy apologies. Just read through the post (and comments) thoroughly and see that it is in fact the same issue, or has at least evolved into the same issue.
However, no solution has been found as of yet...

[markanini]

I realize now it's the "burble/garble" issue reported by jimw for >r30209. I guess his headphones or speakers aren't as as revealing in the trebles as mine and megal0maniac's

Using the 3.9.1 release and setting gain lower is the most acceptable solution for now(further setting sample rate above 64kHz is required to avoid audible aliasing IME).

[megal0maniac]

It's unfortunate, but it looks like the problem was just made worse.
Low level is preferable to noisy recordings. Looks like I'll also be reverting back to the previous version until this has been figured out.

[markanini]

Improvements to recording functionality were added today:
http://www.rockbox.org/tracker/task/11631

EDIT:Despite my whining and moaning recording is a ton better now than perviously. Set 'gain' to 0dB and enjoy! 

[megal0maniac]

Just downloaded r31354-111218 and recording is working perfectly. No noise and recordings can hit 0dB.
Thanks to the developers, Rockbox has made the Clip+ so much more versatile than even the creators probably imagined

Could a moderator please lock this thread?

[Chronon]

Locking at request of OP.