/etc/modprobe.d/blacklist-modem.conf is in alsa-base 1.0.25+dfsg-0ubuntu4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # Uncomment these entries in order to blacklist unwanted modem drivers
# blacklist snd-atiixp-modem
# blacklist snd-intel8x0m
# blacklist snd-via82xx-modem
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