Re^6: Measuring the sound level (dB(A)) with PERL

your code included:


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

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

        # sum the squared distance from the theoretical mean
        $sse += ($v-127.5)**2;
        $cnt++;
    } else {
        print "No byte here\n";
    }
[...]
[download]

The ELSE condition does not show up a single time:

OUTPUT:

root@node:/srv/perl# ./dba2.pl
dbFSrms: -20.9475641203622, dba: 89.0524358796378
dbFSrms: -21.662467195052, dba: 88.337532804948
dbFSrms: -21.5176778028847, dba: 88.4823221971153
dbFSrms: -24.4135001203418, dba: 85.5864998796582
dbFSrms: -23.0140885363105, dba: 86.9859114636895
dbFSrms: -18.5448040737999, dba: 91.4551959262001
dbFSrms: -21.636493545482, dba: 88.363506454518
dbFSrms: -20.3636900956917, dba: 89.6363099043083
dbFSrms: -21.3307953726968, dba: 88.6692046273032
dbFSrms: -22.1928440805489, dba: 87.8071559194511
 [...]
[download]

If there is nothing to read, the read command seems to for something to read.... this seems to be a special behavior of the read command on devices (at least on /dev/dsp1). If there is something to read it will do the calculation as 8000 values were reached (which is 8000 values per second == 8KHz...

Comment on Re^6: Measuring the sound level (dB(A)) with PERL Select or Download Code

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Re^7: Measuring the sound level (dB(A)) with PERL by Monk::Thomas (Friar) on Nov 10, 2016 at 15:49 UTC
Ah. So the read() simply blocks until there actually is something to read and then continues. Which indicates you can either remove the if-condition completely (since it does nothing) -or- replace it with something that acts on the return value (in case there is an actual i/o error).	[reply]
Re^8: Measuring the sound level (dB(A)) with PERL by John-Robie (Novice) on Nov 11, 2016 at 14:05 UTC
That's correct!	[reply]