Audio distorted when BLE is connected

Question

Hello,
we have an android/iOS app on a phone that is connected to my button (nRF51) and to a Bluetooth headset. The app is a kind of walkie talkie that transmit mono audio every time you press the button. What is happen is that if the button is not connected the audio is ok, if the button is connected most of the time the audio is distorted!!! As soon as you turn off the button connection the audio is good again. We did many test and if you don't use the Bluetooth headset but the audio came out directly from the phone , there is no problem. Only if you have both headset and button connected you have the problem!!! There is something I can do? It is really the BLE button connection to use the Bluetooth bandwidth and make the audio distorted? Can I optimize something on my button? 
 thx 
 Enrico

Epasta · Accepted Answer

Hi, the parameters are corrects, because i have seen them on bluetooth guidelines of iOs... 
 "If Bluetooth Low Energy HID is one of the connected services of an accessory, connection interval down to 11.25 ms may be accepted by the Apple product" .( developer.apple.com/.../BluetoothDesignGuidelines.pdf) page 22..
And I am able to connect with all iOs devices... 
 This button can (raise and decrease volume); 
 when i push the button I send notification at mine custom service and characteristic (0x01);
when i release the button i send notification at mine custom service and characteristic (0x02). 
 Is not a problem of distance, because the 3 devices are less then one meter distance. 
 The problem has not a logic, is randomly. 
 Sometimes when i open audio the "audio" is perfect, sometimes is very distorced. 
 What connection interval do you suggest to use? 
 What type of headset are you using?
What type of phone, software and application are you using? 
 Thanks for the time and the help
Regands
Enrico