#!/usr/bin/perl

use strict;
use warnings;
use POSIX qw(log10);

# input device
my $input="/dev/dsp1";

# open filehandler
open(my $fh, '<', $input) or die("ERROR open $input ($!)\n");
binmode($fh);


# 8 bit
# 8000 hertz

my $cnt = 0;
my $value = 0;
my $lastts = 0;
while(1)
{
    if ($cnt == 8000) {
        # the amplitude >= 0 <= 1
        my $amplitude=$value / $cnt / 255;

        # calculate dba = 20 * log10(amplitude / 2 * 10**-5)
        my $dba = 20 * log10($amplitude / 0.00002);
        print "Calculated dB(A): $dba\n";
        $cnt = 0;
        $value = 0;
    }

    my $buffer;

    # read one byte
    read($fh, $buffer, 1);

    if(defined($buffer)) {
        # get an unsigned char
        my $v = unpack("C", $buffer);

        # add the read byte to the values
        $value+=$v;
#       print "Byte read: $v\n";
        $cnt++;
    }
}

close($fh);