Oops, guess I should've specified the ability to look backwards / forwards in the data, hence the substr(). I use the pack/unpack when I don't need to know anything other than a current sample value.

For example, without using arrays or hashes, be able to look forward in the data while processing an waveform:

assuming 16bit/mono:

my $cur_smp = 0;
my $len = length($input_data) / 2;

foreach (unpack("s*",$input_data)) {

  # take the value and add to it the sample value
  # five samples ahead

  if($len < $cur_smp + 5) {
        # if we don't have enough samples left to look ahead,
        # just go with what we've got
     $output .= pack("s",$_);
     $cur_smp++;
     next;
     }

  my $five_ahead = unpack("s",substr($input_data,($cur_smp + 5) * 2,2)
+);

  $output .= pack("s",$_ + $five_ahead);
  $cur_smp++;
  next;
  }

[download]

That substr() is a big hit on large amounts of data, but some sort of look-ahead/back is necessary on things like multi-tap delays and variable delays, and a perl array is out of the question. I'm balking at the math knowledge necessary for PDL, since DSP is a pretty new subject for me, on the low-level aspects of the algorithms.

Would you mind sharing an example of doing the FFT with PDL?

Thanks!
!c

In reply to Re: Manipulating Audio Data in Perl by lofichurch
in thread Manipulating Audio Data in Perl by lofichurch

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.