Cannot get subbands to work with Python

[sebpiq]

Hi again ... sorry for the spam.

I am actually working on a Python wrapper to libxtract to make things more easy ... but as I said in #66 there's a bunch of things I cannot get to work. An example of which is subbands. That might be because I misunderstood something. Here is a sample of code (which needs matplotlib to plot data and numpy) that tries to get things to work. Spectrum apparently works fine (I clearly get a peak at 10 000hz), but subbands is just returning weird results.

from libxtract import xtract
import matplotlib.pyplot as plt
import numpy

def _list_to_doubleArray(a_list):
    mem = a_list
    a_list = xtract.doubleArray(len(mem))
    for i, arg in enumerate(mem): a_list[i] = arg
    return a_list

def _pointer_to_list(pointer, length):
    return [pointer[i] for i in range(0, length)]

sample_count = 2**15
sample_rate = 44100.0
subband_count = 1024
f0 = 10000

# Generate samples
time = numpy.arange(0, sample_count, 1) * 1 / sample_rate
samples = numpy.sin(2 * numpy.pi * f0 * time)

# Calculate spectrum
xtract.xtract_init_fft(sample_count, xtract.XTRACT_SPECTRUM)
spectrum = xtract.doubleArray(sample_count)
argv = [ sample_rate / sample_count, xtract.XTRACT_MAGNITUDE_SPECTRUM, 0, 1 ]
xtract.xtract_spectrum(_list_to_doubleArray(samples), sample_count, _list_to_doubleArray(argv), spectrum)

# Calculate subbands
subbands = xtract.doubleArray(subband_count)
argv = [ xtract.XTRACT_MEAN, subband_count, xtract.XTRACT_LINEAR_SUBBANDS, 0 ]
xtract.xtract_subbands(spectrum, sample_count / 2, _list_to_doubleArray(argv), subbands)

# plot
fig, axes = plt.subplots(nrows=2, ncols=1)
axes[0].scatter(range(0, subband_count), _pointer_to_list(subbands, subband_count))
axes[1].plot(_pointer_to_list(spectrum, sample_count)[sample_count / 2:], _pointer_to_list(spectrum, sample_count / 2))
plt.show()

[sebpiq]

Another weird thing being that if I use XTRACT_SUM instead of mean, I get a nice Segmentation fault (core dumped).

[jamiebullock]

Hi, this isn't spam, but very useful and much appreciated feedback and contribution to the project.

I will look into these issues ASAP.