Experimental awk audio converter for CygWin and AudioScope.sh Post: 302923283

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Top Forums Shell Programming and Scripting Experimental awk audio converter for CygWin and AudioScope.sh Post 302923283 by wisecracker on Friday 31st of October 2014 05:39:31 PM

10-31-2014

Registered User

Experimental awk audio converter for CygWin and AudioScope.sh

Development machine:- Standard MBP 13 inch, OSX 10.7.5...
GNU bash, version 3.2.48(1)-release (x86_64-apple-darwin11)
Copyright (C) 2007 Free Software Foundation, Inc.

Scenario:- Audio capture for AudioScope.sh for CygWin without ANY third party installs.

I am trying my hardest to get a very fast CD quality to 8 bit mono converter for CygWin.
In the process I am learning awk with a difference.

I have a shell version but it is very slow speed wise making it totally unusable for CygWin.

I have a fully working embedded audio capture using SoundRecorder.exe for CygWin using Windows Vista and 7, and I assume 8.x too.
It autosaves as a .WAV file, stereo, 16 bit signed depth at 44100 Hz sampling rate.
There are NO default tools to convert the audio to my usable state so awk is my only way for CygWin.
(There are for OSX and Linux however.)

I needed to convert this to a raw file at quantised 8 bit unsigned depth.

My MBP awk does not have the function strtonum() so the code below is a workaround.
With my limited knowledge of awk, I could only do this in two separate awk stages.

As 'dd' and 'od' ARE part of a default CygWin install then creating a pseudo file was easy.

using 'od' in the script creates a very large file formatted exactly like this:-

Code:

            31148    7375       4  -25735   10869  -24167   14517  -11227
            -6133   -2066    9627  -17687    4971    6743   29567    -635
            -6794  -25374   -2041   26752  -16123   -4752   13322  -30519
            23023  -16552    8628  -31734   -8601   13902    1350    4574
            27658  -16061  -24812    3982   18407   21855  -22704  -24993
            20391    1043   -1924  -32113   11721    -744    4990   28174
           -29418   -9503   26898   19716   -4177  -10850   -6189   -2099
            20053   10576  -25765    2636   11141   -8168  -10572  -15413
            25518   32717    9471  -32754    8971     411   30384   28994
           -22583  -22757    5525  -16048   29524   31623   25504  -17132
           -27344   31565    3412    5296   32543   22148   -7893   19038
            -5604    2076  -24990   27066   25595   -5440  -28169  -19214
            16594    5942   19707   18301  -12918  -31001   -3970    6721
            15475   -1516  -18608   23642   13658    8275   -7287    3707
            21163   -6393   15614   31905   -8726   26653    5264   31329
            27363   10634    1148    6455  -19502  -24530    9748  -22252
            13941  -21525  -25641   32089   13707  -24503  -24055    9336
           -26173  -12437    2745  -10283  -25705  -31137   -3881  -20048

This gave me S1 to $8 per line input where $1, $3, $5 and $7 are the signed 16 bit left hand channel.
$2, $4, $6 and $8 are the 16 bit signed right hand channel.
Thus the first awk script converts the signed 16 bit decimal to unsigned 8 bit decimal, left hand channel only.

The second awk script then converts the unsigned 8 bit decimal to a pure binary file 44100 bytes in size.

It all works and is seriously quick on this MBP but it looks seriously ugly too.

This WHOLE shell script takes around 0.5 seconds to complete:-

Code:

#!/bin/bash
# 16to8bit.sh
> /tmp/left
> /tmp/binary
> /tmp/signed16bit.txt
> /tmp/sample.raw
# Generate a raw pseudo stereo signed 16 bit per channel file, (CD quality).
dd if=/dev/urandom of=/tmp/sample.raw bs=1 count=176400 > /dev/null 2>&1
# Convert to signed dcimal using the default format from 'od'.
od -td2 -An /tmp/sample.raw > /tmp/signed16bit.txt
# Convert, (quantise), the signed 16 bit decimal to 8 bit unsigned left hand channel.
awk 'BEGIN \
{
	FS=" ";
}
{
	if ($1=="")
		exit;
	# $1,$3,$5,$7 are/were the signed 16 bit depth left hand channel.
	# $2,$4,$6,$8 are/were the signed 16 bit depth right hand channel.
	$1=(int(($1+32768)/256));
	# $2=(int(($2+32768)/256));
	$3=(int(($3+32768)/256));
	# $4=(int(($4+32768)/256));
	$5=(int(($5+32768)/256));
	# $6=(int(($6+32768)/256));
	$7=(int(($7+32768)/256));
	# $8=(int(($8+32768)/256));
	printf $1" "$3" "$5" "$7" " > "/tmp/left";
}' < /tmp/signed16bit.txt
# Now create the 44100 byte raw 8 bit depth binary file.
awk --characters-as-bytes 'BEGIN \
{
	BINMODE=3;
	FS=" ";
	n=1;
}
{
	while (n<=44100) \
	{
		printf ("%c",$n) > "/tmp/binary";
		n=n+1;
	}
}' < /tmp/left

Ignore the '\' after BEGIN, etc, as this is my way if making it a little easier for me to read.
Please tear it apart and if there are better methods please point me in the right direction...

Many thanks guys...

I await the flak...

Last edited by wisecracker; 10-31-2014 at 07:06 PM.. Reason: Correct minor spelling errors...

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