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volume control scale - ambiguous positions 47/44/41 #257

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klslz opened this issue May 2, 2019 · 2 comments

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@klslz
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commented May 2, 2019

I discovered while tracing squeezelite volume control that the LMS supplied data do not provide changes on positions 47/44/41 of the VC-100 scale.
The supplied values equal the value of each prior position (48=47, 45=44, 42=41).
All other values on the VC-100 scale are unique though.

This can lead to a shift of up to 3dB in the lower range on e.g. a linear/dB scale.

Ambiguous values should be avoided.

@michaelherger

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commented May 2, 2019

Could this be related?

@klslz

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commented May 2, 2019

That 2-part slope is exactly the curve I see when looking at the 16.16fp data squeezelite
receives from LMS.

My reported issues happen quite a bit above the outlined limits -74dB or 25%.

Your Squeezeplay.pm reference didn't show the actual algorithms.
I did look up the Squeezebox2.pm player now. Because there's a reference in squeezelite slimproto.h in the volume section to it.
And in Squeezebox2.pm I found quite some volume control related maps/formulas and the same curve format.

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