using the command line below I can hear messages from my motorola t80 using channel 7 (446.08125M), sub-code 120

rtl_fm -f 446.08125M -M fm -s 12k -g 19.2 -l 50 | play -r 12k -t raw -e s -b 16 -c 1 -V1 -

but when i try to do the same using pyrtlsdr I get nothing

import numpy as np
import sounddevice as sd
from rtlsdr import RtlSdr


FREQ_HZ = 446.08125e6  # 446.08125 MHz
SAMPLE_RATE = 12e3  # 12 kHz (same as -s 12k)
GAIN = 40  # Gain setting (same as -g 40)
SQUELCH_LEVEL = 50  # Squelch level (same as -l 50)
BUFFER_SIZE = 1024  # Number of samples per batch

sdr = RtlSdr()
sdr.sample_rate = SAMPLE_RATE 
sdr.center_freq = FREQ_HZ
sdr.gain = GAIN

def fm_demodulate(iq_samples):
    phase = np.angle(iq_samples)
    unwrapped_phase = np.unwrap(phase)
    return np.diff(unwrapped_phase)

def process_audio():
    print(f"Listening on {FREQ_HZ/1e6} MHz...")

    while True:
        iq_samples = sdr.read_samples(BUFFER_SIZE)
        fm_audio = fm_demodulate(iq_samples)


        fm_audio = np.clip(fm_audio * 10000, -1, 1)
        if np.max(np.abs(fm_audio)) < SQUELCH_LEVEL / 100: 
            fm_audio[:] = 0

        sd.play(fm_audio, 44100)
        sd.wait()

try:
    process_audio()
except KeyboardInterrupt:
    print("Stopping SDR...")
    sdr.close()

my setup:

• raspberry pi 5
• DVB-T / DAB / FM / SDR USB Stick mit RTL2832U Chipsatz
• motorola t80