From Linux Man Pages
aseqdump - show the events received at an ALSA sequencer port
aseqdump [-p client:port,...]
DESCRIPTION
aseqdump is a command-line utility that prints the sequencer events it receives as text.
To stop receiving, press Ctrl+C.
OPTIONS
-h,--help
Prints a list of options.
-V,--version
Prints the current version.
-l,--list
Prints a list of possible input ports.
-p,--port=client:port,...
Sets the sequencer port(s) from which events are received.
A client can be specified by its number, its name, or a prefix of its name. A port is specified by its
number; for port 0 of a client, the ":0" part of the port specification can be omitted.
CATEGORY