A simple AM radio.

am_radio.py

#!/usr/local/bin/python

from rtlsdr import RtlSdr
import scipy.signal as spsi
from   scipy.io.wavfile import write
import numpy as np

sdr = RtlSdr()

freq_offset = 124996881 # Hz Use this offset when ham-it-up is turned on.
station     =    810396 # Hz
tune_to     = freq_offset + station

seconds    =  5        # Seconds
Fs         = 960000    # Hz  Default: 2.048e6  # 1323000 = 44100 * 30, 
audio_rate = 48000     # Hz 44100 Can't use multiples of this!  Exact sampling rate is needed for this library.

# configure device
sdr.sample_rate = Fs    
sdr.center_freq = tune_to   # Hz
sdr.gain = 32.8             # set to auto to enable AGC
                            # set to a number for manual gain setting.

signal = sdr.read_samples(seconds*Fs) # Note: sample size (seconds*Fs) mustn't be too large
print(signal[0:10])
print(len(signal))

# signal = signal[0::int(Fs/audio_rate)] # Try downsampling before filtering.  
# Doesn't sound as good!  But it saves about 1-second off of total run time of this script.

# http://stackoverflow.com/questions/17833119/lowpass-filter-in-python
N=111
Fc=2000.0/Fs  # = 8000/960000 (8KHz width in relative frequency.)
Fl=  63.0/Fs  # reject below this frequency
h=spsi.firwin( numtaps=N, cutoff=Fc, nyq=Fs/2) # Low pass filter, 2KHz
# h=spsi.firwin( numtaps=N, cutoff=[Fl, Fc], nyq=Fs/2) # Band pass filter, 2KHz  # Doesn't work very well!
filtered=spsi.lfilter( h, 1.0, signal) # 'signal' is the time-series data you are filtering

filtered = filtered[0::int(Fs/audio_rate)]  # down-sampling after filtering sounds much better. 
filtered = abs(filtered)
# filtered = filtered.real # didn't work
print(len(filtered))

# http://stackoverflow.com/questions/10357992/how-to-generate-audio-from-a-numpy-array
scaled = np.int16(filtered/np.max(np.abs(filtered)) * 32767)
write('test.wav', audio_rate, scaled)