问用JTransform库可视化PCM数据

EN

func discrete_time_fourier_transform(aperiodic_audio_wave []float64, flow_data_spec *Flow_Spec) ([]discrete_fft, float64, float64, []float64) {

    min_freq := flow_data_spec.min_freq
    max_freq := flow_data_spec.max_freq

    //      https://www.youtube.com/watch?v=mkGsMWi_j4Q
    //      Discrete Fourier Transform - Simple Step by Step 

    var complex_fft []complex128

    complex_fft = fft.FFTReal(aperiodic_audio_wave) // input time domain ... output frequency domain of equally spaced freqs

    number_of_samples := float64(len(complex_fft))

    nyquist_limit_index := int(number_of_samples / 2)

    all_dft := make([]discrete_fft, 0) // 20171008

    /*
       0th term of complex_fft is sum of all other terms
       often called the bias shift
    */

    var curr_real, curr_imag, curr_mag, curr_theta, max_magnitude, min_magnitude float64

    max_magnitude = -999.0
    min_magnitude = 999.0
    min_magnitude = 999.0

    all_magnitudes := make([]float64, 0)

    curr_freq := 0.0
    incr_freq := flow_data_spec.sample_rate / number_of_samples

    for index, curr_complex := range complex_fft { // we really only use half this range + 1

        // if index <= nyquist_limit_index {
        if index <= nyquist_limit_index && curr_freq >= min_freq && curr_freq < max_freq {

            curr_real = real(curr_complex) // pluck out real portion of imaginary number
            curr_imag = imag(curr_complex) // ditto for im

            curr_mag = 2.0 * math.Sqrt(curr_real*curr_real+curr_imag*curr_imag) / number_of_samples

            curr_theta = math.Atan2(curr_imag, curr_real)

            curr_dftt := discrete_fft{

                real:      2.0 * curr_real,
                imaginary: 2.0 * curr_imag,
                magnitude: curr_mag,
                theta:     curr_theta,
            }

            if curr_dftt.magnitude > max_magnitude {

                max_magnitude = curr_dftt.magnitude
            }

            if curr_dftt.magnitude < min_magnitude {

                min_magnitude = curr_dftt.magnitude
            }

            // ... now stow it

            all_dft = append(all_dft, curr_dftt) 

            all_magnitudes = append(all_magnitudes, curr_mag)
        }

        curr_freq += incr_freq
    }

    return all_dft, max_magnitude, min_magnitude, all_magnitudes
}