Problem solved! (mostly) Someone in the Android Developers forum suggested that I open my audio channel with an option that supposedly bypasses AGC and filtering. It is called MediaRecorder.AudioSource.VOICE_RECOGNITION in the Android SDK. When I did that the aliasing artifacts vanished. All I see now is one nice peak in the FFT regardless of frequency. So apparently there was something in the AGC or noise cancellation processing that introduced the problem. I guess the only thing I am sacrificing now is AGC, but for my app I don't think that is a problem. -Robert Scott Hopkins, MN
Android phone sample rate DSP puzzle
Started by ●February 8, 2016
Reply by ●February 9, 20162016-02-09
Reply by ●February 10, 20162016-02-10
On Tuesday, February 9, 2016 at 9:34:26 PM UTC-5, Robert Scott wrote:> Problem solved! (mostly) > > Someone in the Android Developers forum suggested that I open my audio > channel with an option that supposedly bypasses AGC and filtering. It > is called > > MediaRecorder.AudioSource.VOICE_RECOGNITION > > in the Android SDK. When I did that the aliasing artifacts vanished. > All I see now is one nice peak in the FFT regardless of frequency. So > apparently there was something in the AGC or noise cancellation > processing that introduced the problem. I guess the only thing I am > sacrificing now is AGC, but for my app I don't think that is a > problem. > > -Robert Scott > Hopkins, MNFYI: a 2011 post on the android-platform forum: https://groups.google.com/forum/#!topic/android-platform/2ZJFBjJOZV0 Kevin