Audio Analysis in Extempore

[Jason Levine]

Hi all, 

I'm hoping to use Extempore in my latest audiovisual commission.  So I need to learn how to get samples from the DSP closure into functions from libraries like libXtract or aubio.  I figured I would teach myself by studying the spectral_meter.xtm example, but unfortunately it does not compile, complaining of:

Compiler Error cannot find symbol  fft_cpxd

in this function:

;; take the time_domain signal (time_buffer) and return the spectrum

(bind-func mag_spectrum



  (let ((nbins 512) ; number of bins for spectrogram

        (spectrum:double* (zalloc nbins))

        (i:i64 0))

    (lambda (audio:double* fft_window_size time_buffer freq_buffer)

      (dotimes (i fft_window_size)

        ;; add sum of L and R channels into real component

        ;; of time_buffer (which is a buffer of complex values

        (tset! (pref-ptr time_buffer i) 0

               (+ (pref audio (* 2 i)) ; L channel

                  (pref audio (+ 1 (* 2 i)))))) ; R channel

      ;; take DFT, store results in freq_buffer

      (fft_cpxd time_buffer freq_buffer fft_window_size)



      (bin_spectrum spectrum freq_buffer fft_window_size nbins))))

Is it possible that the FFT library has changed since the example was created?

Nonetheless I see where the audio samples are being passed to the spectrum analyzer in dsp.  How could I change this to to use the samples from "in" (for live input) instead of an audio file?

(bind-func dsp:DSP 100000000 ; make sure we allocate enough memory



  (let ((audio_length 60)

        (audio:double* (zalloc (* 44100 2 audio_length)))

 (samples_read (read_audio_data "/path/to/audiofile.wav"

                                       audio

                                       0

                                       (* 44100 audio_length)))

        (playhead 0)

        (fft_window_size 1024)

        (time_buffer:cpxd* (zalloc fft_window_size))

        (freq_buffer:cpxd* (zalloc fft_window_size))

        (i:i64 0))

    (lambda (in time chan dat)

      (if (and (= (modulo playhead fft_window_size) 0)

               (= chan 0.0))

          (mag_spectrum (pref-ptr audio playhead) fft_window_size

                        time_buffer freq_buffer))

      ;; increment playhead once per (stereo) pair of samples

      (if (= chan 1.0)

          (set! playhead (modulo (+ playhead 1)

                                 (* audio_length 44100))))

      ;; play audio

      (pref audio (+ (dtoi64 chan) (* 2 playhead))))))

Thanks and please let me know if you know how to fix the spectral_meter.xtm example!

Jason