using byte array from audiorecord in fft

How do I use the byte array from AudioRecord lib with this configuration :
AudioSource=AR.A_Src_Mic
SampleRate=44100
ChannelConfig=AR.Ch_Conf_Mono
NoChnls=1
AudioFormat=AR.Af_PCM_16
BitsPerSample=16
In fft lib. ?
I have to feed the fft.Transform2(data from audiorecord, FFTReal, FFTImag) function with double array ,
I don`t understand how to convert the byte array to double(not with the DoublesFromBytes function from ByteConverter lib)