BC127 Automatic Gain Controle

Dear All,

I’ll do a second try to get some help for my problems with the BC127 module.

I am having an application with analog audio signals that needs beeing transfered by bluetooth to a headset.
The still existing problem is that for some reason Audio signals are mixed with noise, so the signal to noise ratio becomes bad and sound is bad as well.

After a long period of testing with different setups and different hardware now I am pretty shure, that there must be something like an ‘automatic gain control’ which I connot disable. The reason why I am sure is that when I feed in a ‘normal’ audio level, then the headset volume is OK and seems to be steady. When I reduce the input signal level, then mostly the headset volume goes down at first, but then it becomes louder again, mixed with the noise.

Is there anybody from SIERRA side who can explain this behaviour and let me know how I can disable this functionality?

Any help is much appreciated


Hi Crothe,

I’m having this same issue, I’m also waiting for their reply on this regard. Please let me know though if you discover something, thanks! :slight_smile:


Hi João,

good to hear that I am not the only one, fighting with a ghost :skull:
… so it is really a problem that comes up for some reason.

I use the BC127 in different setups, some of them do not have this problem (e.g. simple audio streaming with A2DP) but I have it always when using the AGHFP profile with a bad quality audio signal (much noise, klicks, crackling in the signal). What I am thinking is, that this effect is initiated by the type of audio signal, maybe higher frequent peaks or so…

What is your experience and how would you explain the problem in your words?


Hi Christian,

For me, the stream that is showing the problem is actual when using the A2DP (but probably not noisy as yours, just with undesired processing), but I haven’t tried other configurations yet. Even though we’re both, probably seeing some automatic gain control, I think we’re seeing it through different scenarios.

My problem description can be found here, if you want to have a look: NREC Enabling/Disabling flag

But shortly put into words, on my case, is the DSP that seems to be applying some noise suppression even when I disable it. Which seems to be very similar to the problem you mention where your headset volume is going down and then back up. Have you tried feeding a more flat signal (e.g. white/pink noise)? Because in your case it seems that the algorithm is trying to compensate for the noise, so it ends up affecting the main signal as well. (regarding the pops, I have no explanation. Are you feeding into via analog or digital path?)



I am having the same problem in AGHFP. Lots of background noise and and a constant beeping/buzzing sound.

Any advice to get rid of it would be appreciated!