only MP3 outputs silent - file contains just LAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU repeated

[alecmyers]

Summary: UDP output has correct audio, but all MP3 outputs are silent

version is 4.1.1. on RPi4B, compile flags are -DPLATFORM=armv8-generic

Frequency is set to local ATIS to produce continuous audio output.

Results:

• udp stream to local produces correct audio (which can be streamed to icecast with ffmpeg)
• direct icecast stream output is silence (stream connects correctly)
• file output contains repeated string LAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU...
  i.e. looks like this: UUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.100UUUUUUUUUU????HUUUUUUUUUUUUUUUUUUUUUUUUUUU
• file plays back as silence

Seems like all MP3 coding is failing somewhere. Is this a problem with libmp3lame, or with RTLSDR-Airband? I'm not confident enough in the latter possibility to file a bug report. Any suggestions gratefully accepted.

dpkg -s libmp3lame-dev reports:

Package: libmp3lame-dev
Status: install ok installed
Priority: optional
Section: libdevel
Installed-Size: 732
Maintainer: Debian Multimedia Maintainers [email protected]
Architecture: arm64
Multi-Arch: same
Source: lame
Version: 3.100-3
Depends: libmp3lame0 (= 3.100-3)

The RTLSDR-airband config is as follows:

devices:
({
type = "rtlsdr";
index = 0;
gain = 45;
centerfreq = 133.55;
correction = 0;
sample_rate = 1.0;
channels: (
{
freq = 133.6;
lowpass = 200;
highpass = 4000;
squelch_threshold = -44;
outputs: (
{
type = "icecast";
server = "127.0.0.1";
port = 8000;
mountpoint = "xxx.mp3";
name = "xxx";
genre = "ATC";
username = "xxx";
password = "xxx";
},
{
type="file";
directory="/opt/xxx";
filename_template="xxx";
continuous=false;
include_freq=false;
append=true;
},
{
type = "udp_stream";
dest_address = "127.0.0.1";
dest_port = 9001;
continuous = true;
}
);
}
);
}
);

[charlie-foxtrot]

I think your highpass / lowpass are flipped. highpass will pass frequencies higher than what is specified, lowpass will pass frequencies lower than what is specified. Not too many frequencies that are below 200Hz while at the same time above 4 kHz ;)

NOTE: highpass / lowpass only applies to the MP3 output and not to the UDP stream

[alecmyers]

D'oh! Thank you. Hours of my life spent chasing that one!

[charlie-foxtrot]

so others dont hit the same issue: #399