Take the data, apply the FFT, store the data.But you have provided no details for anything concrete...Convert with what? Store in what format? What sample depth and rate?
If i speak trough a microphone , can i store the data in FFT?
What kind of format will this be? txt data where the binary things are stored or a .fft data ?
FFTs are done on a data set that is a multiple of a power of two. So something like chunks of 128,256, ore 512 samples at a time.So to take the FFT of 10 seconds of audio, you have to record onto an SD card, then take the samples out say 256 at a time, do the FFT and then save it back into another file. The FFT needs space to work things out and you can't make the frames too big on an Arduino.What do you want to do with this FFT data?
i want that the device can recognition a wave form of a human speech and then search for the pair in the SD-card.
Ah, speech recognition. I think you should be prepared for disappointment here. No two speech sample will produce identical transforms so the searching you will have to do with be fuzzy. That is at best give you the probability of a match. And this is only if you can synchronise the start of your recording with the start of the recording of the template you are matching against.If speech recognition were that easy they would have cracked by now.
would it work?
No.The amount of sound you can take an FFT of is in the order of microseconds. The exact number depends on the sample rate. Taking a sequence of samples and then taking the FFT and then repeating it will leave holes in the sound recorded.If you want to look at an FFT then get the free app called Audacity, that will run on a laptop and will give you a feel of the repeatability of an FFT and sound recording.