Receive volume is slowly goes down using LoudnessEnhancer

[Naaman Sittsamer]

I'm not sure that this is the right forum for this issue.... but for now -

Hi,

I'm using LoudnessEnhancer audio effect for voice calls.

I've found out that on a long call (few hours) the output volume is slowly goes down, until it's very hard to hear anything.

After digging into the code I think the problem is in the DRC module (dynamic_range_compression.cpp).

When monitoring "compressor_gain_" we can see that its maximal value decreases in time (starts at 1.0).

I think the reason for that is the math-limitations of the processor compared to the source code (the theoretical algorithm).

E.g. - the machine cannot truly handle 0.008333333333333333217685101601546193705871701240539550781250f that the Taylor approximation function is using.

A workaround for this issue is something like -

@@ -121,6 +121,8 @@ void AdaptiveDynamicRangeCompression::Compress(float *x1, float *x2) {

   }

   compressor_gain_ *=

       math::ExpApproximationViaTaylorExpansionOrder5(state_ - prev_state);

+  if ((compressor_gain_ > 0.999f) && (compressor_gain_ < 1.001f))

+         compressor_gain_ = 1.0f;

   *x1 *= compressor_gain_;

Is it a known issue?

Thanks,

Naaman

[Phil Burk]

Hello Naaman,

Thanks for pointing this out. It does look like there might be some issues with the code that could cause a drift over time.

I have filed a bug internally for Android. We will investigate.

Thanks,

Phil Burk

[Naaman Sittsamer]

Hi Phil,

I'll be happy if you could (later) share Android analysis for this issue, especially if there's a patch to fix it.

Thanks,

Naaman