Option to replace hardware volume control with software volume control

[LEDavid90]

Dear Rockbox Developers,

thank you very much for your great work! Please don't misunderstand me, it's just an "idea" if any programmer might consider it interesting (unfortunately I'm not able to handle source code):

When playing .ogg files in Rockbox with my Sansa Fuze V2, changing the volume (especially at higher values) causes some kind of "clicking noise" (this also happens with .mp3 files, but to a lower extent).
By contrast, using the equalizer precut (which I asume to be software controlled) does not effect this noise.

So far I can use a workaround, setting the EQ precut as left and right quick screen item, however if it were not too complicated and someone able to do this could create a patch which (optionally) replaces hardware volume control by software volume control, this would be great. 

However I don't know how important this problem is for the developers (and on how many other devices it appears).


David

[saratoga]

There shouldn't be a clicking noise, and I've never noticed one on the Sandisk players before.  The devices have hardware that is supposed to suppress any noise on gain change.  Not sure why it wouldn't be working for you.  Does it happen in the sandisk firmware?

We do actually have the ability to implement volume control in software.  Its controlled by the define "HAVE_SW_VOLUME_CONTROL".  However, if you just turn it on in a device that has hardware volume control I suspect a lot of things will break. 

[dreamlayers]

Noise might come from I2C communication with the codec chip.

If your headphones have a volume control, what happens if you turn that down and turn up device volume? If you have no volume control on headphones and no inline volume control on a separate cord, what happens with different headphones? Some kinds of noise are only noticeable on low impedance high efficiency headphones.

[LEDavid90]

Thanks a lot for your replies! In fact that problem does only appear when using headphones (two cheap in-ears from Sennheiser and an also rather cheap headphone called "KOSS Porta Pro"), whereas connecting my Sansa Fuze to my stereo system, I could not notice this clicking noise. So it seems to be an impedance issue.

Which is also interesting for me: Every third step of volume change this noise does not appear.

And according to what you, saratoga, wrote, it is not as simple to replace standard volume control by software volume control as I supposed. What did you mean by "a lot of things will break" (by just activating "HAVE_SW_VOLUME_CONTROL")? Would this also affect the hardware, or would it be possible (and sufficient to solve possible problems) to restore a backup of the previously installed Rockbox configuration?

[saratoga]

Which is also interesting for me: Every third step of volume change this noise does not appear.

Every third volume change is ignored since the Fuze only has 1.5 dB gain resolution on the amplifier.

What did you mean by "a lot of things will break" (by just activating "HAVE_SW_VOLUME_CONTROL")?

You'll probably have to fix the code or it won't compile. 

[LEDavid90]

Every third volume change is ignored since the Fuze only has 1.5 dB gain resolution on the amplifier.

Ah, that makes it clear for me! Thanks for this helpful background information.

You'll probably have to fix the code or it won't compile.

So it wouldn't even be applicable with only the change mentioned before. OK, then I would have to become more familiar with programming in C, I guess. 


As I just noticed, this noise only did not appear using my stereo system because I had turned off the equalizer before testing it. With EQ activated, applying a bit of bass boost, this noise was reproducable with my stereo system as well, whereas it did not appear using the headphones without EQ.