is there a way to filter audio in android system?
I am interested to get only the audio of a fixed frequency.
If you get your audio via the AudioRecord class, then you'll have raw audio data that you could filter using whatever audio filter algorithm you have. Or are you looking for an audio filtering library?
As Dave says, the AudioRecord class is the easiest way. Often times, I will extend an AsyncTask that implements AudioRecord to read the audio buffer and push the buffer back to the UI thread for visualization (if needed).
Regarding the filtering of the audio, Android does not provide any built-in way of doing this. The way you would filter out certain frequencies is by taking the Fourier Transform of the sampled audio and then pulling out the frequencies of interest.
If you want more details on filtering, you should probably post a new SO question or wiki the Fast Fourier Transform (FFT). You might also look into JTransforms which is a great open source FFT library that runs wonderfully on Android.
Please do NOT use the FFT for this. That's amateur hour. (The FFT is a great tool with many great use-cases, but this is not one of them.) You most likely want to solve this problem using time domain filters. Here's a post to get you started writing your own filters in the time domain as easy as can be. However, a lot of people stumble on that since it's a bit specialized, so if you want to use something built-in to android, start with the equalizer audio effect.
Related
I am using this code I found to record mic audio, I am not writing the data into the PCM file, I simply write the data to a ByteArrayOutputStream variable: Android AudioRecord example
When I finish the record, I have a byte array. How should I analyze the byte array using FFT? Simply speaking, I am trying to analyze a FSK sound wave.
I think that I understood your question now. You want to know how to decode a FSK Signal with android? And to do this you want to use the FFT?
You can achieve this without the FFT.
Android Demo App
There is the source code of an Android App that implements FSK Modulation/Demodulation.
The FSKModule.java implements a decoder that uses 3150Hz/1575Hz as mark/space. The important methods are findStartBit, parseBits, processSound and countPeaks. The implementation simply counts the number of peaks within a time slice. With the number of peaks you can infer to the corresponding frequency and decode the signal. This is easier and faster than using FFT.
Why not using FFT?
There is a nice blog that describes when to (not) use the FFT. (e.g. Why EQ Is Done In the Time Domain and other interesting things)
I am working on an application. Here I want to read various sounds using Android Application. I know how to record in Android. Now what I want to do is to read a sound and based on its frequency I want to display it on Android Screen. So how can I read the frequency in Hz or KHz?
You will need to perform a discrete Fourier transform on your recorded audio samples. You can write code yourself or use a library for it. Unfortunately I have no idea which FFT libraries exist for Java, but I am sure you can google that. I found two in 2 minutes:
http://www.ee.ucl.ac.uk/~mflanaga/java/FourierTransform.html
https://sites.google.com/site/piotrwendykier/software/jtransforms
I want to develop an android app that takes in the audio signal and generates the time and frequency domain values.
I have the audio in a buffer which is obtained from the android MIC. I want to use this buffer values to generate a frequency domain graph. Is there some code that would help me find the FFT of an audio signal??
I have seen Moonblink's Audalyzer code and there are some missing components in the code. I could find lots of missing modules. I want to find a better logic that would take in audio and perform some calculations on it.
I found these for you using duckduckgo:
Android audio FFT to retrieve specific frequency magnitude using audiorecord
http://www.digiphd.com/android-java-reconstruction-fast-fourier-transform-real-signal-libgdx-fft/
This should help
I want to develop a bass effect for media player.Can any body help me regarding this..
First step is to isolate the low-frequency components. You will need an FFT to do this... there's one linked to this older S/O question.
After you've got the frequency representation of your audio data, alter the magnitudes of the low-frequency components as you see it, run the inverse transform to convert it back to audio samples, and pass it to the audio hardware for playback.
android people..
I have already gone through answers of no. of question in stackoverflow , many of them are little bit similar to my problem. but i could not get solution of my problem.
problem is that .
In my Application i want to Rotate an Image until noise is coming from the microphone of Device and i don't want to save the audio file.
so , How can i start or implement this if anyone know the link or hint that how to implement this thing.
Thanks..
You can use the AudioRecord class to access the audio stream from the microphone. Than you can try to detect noise from that bitstream. After calling startRecord on the AudioRecord you have to use read to read the bytes from the stream (and you have to do that fast enough such that the internal buffer is not overflowing). You'll get 16bit integers from that stream which you can use to analyze basically the noise level. However recognizing a specific sound is not as easy.