Clip+ DC offset

[saratoga]

I just noticed on my Fuze that when it's paused adjusting the volume level results in a distinct clicking sound that can be heard at each volume increment at the upper levels. 

If you have a DC offset and you change it, thats will produce a click sound. 

[bertrik]

Two things I'd like to reply on: 1) clicks/beeps on volume change 2) DC offset. IMO, these are related, but different things.

Regarding 1), there is a ZCU bit (zero-cross update) in the audio codec used in the AMS sansas. This bit should apply volume changes only on a zero crossing (when the amplitude is near zero). I have no idea though if we currently use it. Also if enabled, I don't know if the volume change is applied anyway when no zero crossing happens, I vaguely remember from reading the AMSv2 codec specifications that a volume change is applied anyway within a few ms if there is no zero crossing.
Solution: check in the code if we use the ZCU mechanism and enable it if not, possibly check what the OF does.

Regarding 2), the AMS sansas (both AMSv1 and AMSv2) use a capacitor-less system of connecting the amplifier to the headphones. They also use a kind of virtual ground for the headphones. Things we could do here is (just some ideas): 1) send a 0-sample after the last sample 2) check the datasheet to see if we can power down the codec with 0 DC output (but probably we want audio to stay enabled for voice when paused)  3) check the datasheet for other ideas.

[mc2739]

Regarding 1), there is a ZCU bit (zero-cross update) in the audio codec used in the AMS sansas. This bit should apply volume changes only on a zero crossing (when the amplitude is near zero). I have no idea though if we currently use it.

In current SVN, ZCU is set to off for AS3525 (AMSv1) devices. (firmware/drivers/audio/as3514.c - line 205)

ZCU is enabled for non-AS3525 devices.  AS3543 (AMSv2) does not appear to have ZCU.