Well if that don't beat all! It worked! I just replaced MediaRecorder.AudioSource.MIC with MediaRecorder.AudioSource.VOICE_RECOGNITION in my "new AudioRecord(...)" and now the artifacts around 4000 Hz are gone. I can sweep a tone above and below 4kHz and all I get is one nice peak in the FFT. Thanks a lot for the suggestion. Now I just need to test and see if my app will suffer due to the loss AGC.
-Robert Scott Hopkins, MN On Tuesday, February 9, 2016 at 5:29:00 PM UTC-6, Julian Bunn wrote: > > I think that you should perhaps use the VOICE_RECOGNITION stream which is > *supposed* to be devoid of filtering and AGC etc.. > > > http://developer.android.com/reference/android/media/MediaRecorder.AudioSource.html#VOICE_RECOGNITION > > It's possible to select which Mic is being used, too. (My app offers a > choice between "FRONT" and "Main" mics - the Front one is typically next to > the front facing camera lens, and makes sense for video ...) > > > > On Tue, Feb 9, 2016 at 1:19 PM, 'RLScott' via Android Developers < > [email protected] <javascript:>> wrote: > >> No, I don't know anything about the "VOICE_RECOGNITION" mic stream. I am >> just using the standard audio input stream set up with the code I posted >> earlier. However someone in a DSP forum told me that the LG G3 has two >> mics, one in front and one in back, and they do some DSP with those two >> data streams to realize noise cancellation. This might be some artifact of >> that operation. >> >> -Robert Scott >> Hopkins, MN >> >> On Tuesday, February 9, 2016 at 1:20:12 PM UTC-6, Julian Bunn wrote: >>> >>> That is very curious! Are you using the "VOICE_RECOGNITION" mic stream? >>> I'm wondering if there is some sort of odd DSP filtering being applied in >>> the firmware. >>> >>> On Tue, Feb 9, 2016 at 8:59 AM, 'RLScott' via Android Developers < >>> [email protected]> wrote: >>> >>>> OK, I finally got myself a cheap LG G3 from eBay and did some testing. >>>> The situation is not exactly as I described before. Here is what is >>>> really >>>> happening. I tested my app with a sine-wave tone generator. >>>> >>>> When the tone generator is below about 3700 Hz, the spectrum displayed >>>> in my app shows just one peak at the desired frequency. As the frequency >>>> of the tone generator increases toward 4000 Hz, a very tiny mirror image >>>> peak begins to appear on the other side of 4000 Hz. It gradually gains in >>>> amplitude until by 3958 Hz, the amplitude of the image peak is actually a >>>> bit higher than the peak at the correct frequency. As the tone goes above >>>> 4000 Hz, the image peak appears below 4000 Hz, and gradually decreases in >>>> amplitude as the tone frequency increases. I ran the tone frequency up to >>>> 4698 Hz and saw a single peak at 4698 Hz in the spectrum and no image >>>> peak. This entirely destroys my supposition that this phone is initially >>>> sampling at 8000 Hz and then up-sampling to 44100, because if it were, >>>> there would be no way to show a single peak at 4698 Hz with no image peak, >>>> right? I mean, the information that discriminates between 4698 and 3302 >>>> is >>>> totally destroyed if the audio is initially sampled at 8000 Hz. >>>> >>>> But something is going on in the phone's audio system that introduces >>>> this image around 4000 Hz. Could it be some sort of hetrodyning? I know >>>> in single sideband radio there are ways to invert the audio spectrum if >>>> the >>>> detection carrier is set on the wrong side of the signal. But why would >>>> things return to normal for tones well away from 4000 Hz? >>>> >>>> -Robert Scott >>>> Hopkins, MN >>>> >>>> >>>> On Tuesday, February 2, 2016 at 12:41:32 PM UTC-6, Julian Bunn wrote: >>>>> >>>>> Perhaps you can post your code, and we can take a look to see if we >>>>> see anything that might be causing this problem? Otherwise, if it really >>>>> is >>>>> a firmware "feature" in those two devices, I don't see any good >>>>> alternatives other than a) marking your APK as incompatible with those >>>>> devices in Google Play, or b) doing some DSP in your software to detect >>>>> the >>>>> condition and work around it somehow. If it were me, I would obtain a G3 >>>>> and start testing ... >>>>> >>>>> >>>>> >>>>> On Tue, Feb 2, 2016 at 6:08 AM, 'RLScott' via Android Developers < >>>>> [email protected]> wrote: >>>>> >>>>>> The theory says if the initial hardware sampling is done at 8000 >>>>>> samples per second, the aliasing is already "frozen" into the sampled >>>>>> data. >>>>>> You can see that by observing that 4100 Hz and 3900 Hz look exactly the >>>>>> same - produce exactly the same samples - after they are sampled at 8000 >>>>>> samples per second. No amount of digital signal processing after that >>>>>> point can distinguish the two cases, so the aliasing in the up-sampled >>>>>> FFT >>>>>> is inevitable, with or without windowing. >>>>>> >>>>>> I may yet get a G3 on Ebay as you say, but I was hoping for some >>>>>> independent confirmation of this problem with a codebase that had >>>>>> nothing >>>>>> in common with my code, in case there is something I am doing in the >>>>>> code >>>>>> that is making the difference. So if you have an app that processes >>>>>> sound >>>>>> and can detect frequency content above 4000 Hz, just have someone with >>>>>> one >>>>>> of these failing devices go to piano and play the highest "B". That is >>>>>> usually about 4019 Hz. If the device is failing as I predict, there >>>>>> should >>>>>> also be an indication of a tone at 3981 Hz. >>>>>> >>>>>> Robert Scott >>>>>> Hopkins, MN >>>>>> >>>>>> On Sunday, January 31, 2016 at 1:39:58 PM UTC-6, Julian Bunn wrote: >>>>>> >>>>>>> If you are only getting 8000 sps then even with interpolation to >>>>>>> 44100 you would never see any signal above 4000Hz in an FFT, right? Are >>>>>>> you >>>>>>> windowing the FFT? >>>>>>> >>>>>>> If there are truly problems like this with the audio firmware on the >>>>>>> LG G3 and Nexus 7, I haven't heard any reports from my users about >>>>>>> them. >>>>>>> That's not to say there can't be an issue, of course :-) If I were you, >>>>>>> I >>>>>>> would obtain a cheap used G3 on Ebay to test with. >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Saturday, January 30, 2016 at 6:13:08 PM UTC-8, RLScott wrote: >>>>>>>> >>>>>>>> But are you sure you are getting the sample rate you asked for? >>>>>>>> How would you know? As you can see from my very first posting, all >>>>>>>> the >>>>>>>> checks you are doing here work fine for me too, and I actually do get >>>>>>>> the >>>>>>>> number of samples per second I ask for. But they are not true >>>>>>>> samples. >>>>>>>> They have been faked by up-sampling. The system takes 8000 samples per >>>>>>>> second and then duplicates each sample enough times to make up 44100 >>>>>>>> or >>>>>>>> 22050 or whatever. But I know those samples are not true samples >>>>>>>> because I >>>>>>>> see aliasing around 4000 Hz in the frequency spectrum. Unless you >>>>>>>> specifically look for this problem by testing with a pure tone above >>>>>>>> 4000 >>>>>>>> Hz and analyze with an FFT and look for aliasing below 4000 Hz, >>>>>>>> everything >>>>>>>> will appear fine. Again this only happens on a very few models - >>>>>>>> specifically the LG G3 and the Asus Nexus 7. >>>>>>>> >>>>>>>> On Wednesday, January 27, 2016 at 10:57:45 AM UTC-6, Julian Bunn >>>>>>>> wrote: >>>>>>>>> >>>>>>>>> Yes, that looks fine to me ... In case it helps, here is a snippet >>>>>>>>> of what I do to check a samplerate is going to work: >>>>>>>>> >>>>>>>>> minBuffer = AudioRecord >>>>>>>>> .getMinBufferSize(rate, config, encoding); >>>>>>>>> if (minBuffer != AudioRecord.ERROR_BAD_VALUE >>>>>>>>> && minBuffer != AudioRecord.ERROR) { >>>>>>>>> boolean bGood = true; >>>>>>>>> try { >>>>>>>>> audio = new AudioRecord(audioSource, rate, config, >>>>>>>>> encoding, minBuffer); >>>>>>>>> int istate = audio.getState(); >>>>>>>>> if (istate != AudioRecord.STATE_INITIALIZED) >>>>>>>>> bGood = false; >>>>>>>>> } catch (Exception e) { >>>>>>>>> bGood = false; >>>>>>>>> } >>>>>>>>> audio.release(); >>>>>>>>> audio = null; >>>>>>>>> if (bGood) >>>>>>>>> return rate; >>>>>>>>> >>>>>>>>> >>>>>>>>> On Tuesday, January 26, 2016 at 12:49:46 PM UTC-8, RLScott wrote: >>>>>>>>>> >>>>>>>>>> I am calling >>>>>>>>>> AudioRecord.getMinBufferSize(44100,AudioFormat.CHANNEL_IN_MONO,AudioFormat.ENCODING_PCM_16BIT) >>>>>>>>>> >>>>>>>>>> and using the returned minAudioRecordBufSize in >>>>>>>>>> >>>>>>>>>> new AudioRecord(MediaRecorder.AudioSource.MIC, >>>>>>>>>> 44100,AudioFormat.CHANNEL_IN_MONO, >>>>>>>>>> AudioFormat.ENCODING_PCM_16BIT, >>>>>>>>>> minAudioRecordBufSize); >>>>>>>>>> >>>>>>>>>> Is that sizing the buffers correctly? >>>>>>>>>> >>>>>>>>>> Thanks for the offer for the enumeration app, but I do not have a >>>>>>>>>> failing device at my disposal. Only a few devices are failing, and >>>>>>>>>> they >>>>>>>>>> are all owned by my customers. I can't ask too much of them in the >>>>>>>>>> way of >>>>>>>>>> debugging help. >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On Friday, January 15, 2016 at 1:34:15 AM UTC-6, Julian Bunn >>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>> Make sure you are sizing the buffers correctly i.e. respecting >>>>>>>>>>> the minimum recording buffer size (in bytes) required. If you don't >>>>>>>>>>> then I >>>>>>>>>>> believe the system will drop you down to 8kHz sample rate, which is >>>>>>>>>>> what >>>>>>>>>>> you are seeing (I think?). >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> On Wednesday, December 23, 2015 at 9:52:37 AM UTC-8, Robert >>>>>>>>>>> Scott wrote: >>>>>>>>>>>> >>>>>>>>>>>> I first call *AudioRecord.getMinBufferSize(22050...* If this >>>>>>>>>>>> returns an error (<1) then I call >>>>>>>>>>>> *AudioRecord.getMinBufferSize(44100...* Whichever one of >>>>>>>>>>>> these calls succeeds, I use that rate in my call to "*new >>>>>>>>>>>> AudioRecord(..,sampleRate..)*" >>>>>>>>>>>> >>>>>>>>>>>> I don't actually have one of these misbehaving devices, so my >>>>>>>>>>>> experiments so far have been with the help of my customers. >>>>>>>>>>>> >>>>>>>>>>>> -Robert Scott >>>>>>>>>>>> Hopkins, MN >>>>>>>>>>>> >>>>>>>>>>>> -- >>>>>> You received this message because you are subscribed to a topic in >>>>>> the Google Groups "Android Developers" group. >>>>>> To unsubscribe from this topic, visit >>>>>> https://groups.google.com/d/topic/android-developers/4yG4_Gw4Ilc/unsubscribe >>>>>> . >>>>>> To unsubscribe from this group and all its topics, send an email to >>>>>> [email protected]. >>>>>> To post to this group, send email to [email protected]. >>>>>> Visit this group at >>>>>> https://groups.google.com/group/android-developers. >>>>>> To view this discussion on the web visit >>>>>> https://groups.google.com/d/msgid/android-developers/6b7520f2-8376-4f1c-9f84-8f7f310846ae%40googlegroups.com >>>>>> >>>>>> <https://groups.google.com/d/msgid/android-developers/6b7520f2-8376-4f1c-9f84-8f7f310846ae%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> >>>>> -- >>>> You received this message because you are subscribed to a topic in the >>>> Google Groups "Android Developers" group. >>>> To unsubscribe from this topic, visit >>>> https://groups.google.com/d/topic/android-developers/4yG4_Gw4Ilc/unsubscribe >>>> . >>>> To unsubscribe from this group and all its topics, send an email to >>>> [email protected]. >>>> To post to this group, send email to [email protected]. >>>> Visit this group at https://groups.google.com/group/android-developers. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/android-developers/ecdce8c1-e5a8-463d-a9f6-6852749e6c34%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/android-developers/ecdce8c1-e5a8-463d-a9f6-6852749e6c34%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >> You received this message because you are subscribed to a topic in the >> Google Groups "Android Developers" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/android-developers/4yG4_Gw4Ilc/unsubscribe >> . >> To unsubscribe from this group and all its topics, send an email to >> [email protected] <javascript:>. >> To post to this group, send email to [email protected] >> <javascript:>. >> Visit this group at https://groups.google.com/group/android-developers. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/android-developers/c5530388-6a11-4e52-890e-94ae55dd7a78%40googlegroups.com >> >> <https://groups.google.com/d/msgid/android-developers/c5530388-6a11-4e52-890e-94ae55dd7a78%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "Android Developers" group. 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