NAME
Audio::Mix - Module for fading cross-fading wav audio files.
SYNOPSIS
my $settings = {
'out_dir' => '.',
'hints' => {
'dir' => '.',
'mode' => 'write',
},
'fade_time' => 15,
'default_fade' => 'linear',
};
my $wav = Audio::Mix -> new( $settings );
my $xfade = {
'out_type' => 'cooledit',
'read_dir' => './t',
'out_file' => 'xfade',
'dao_file' => 1,
};
$wav -> mix( $xfade );DESCRIPTION
Perl Wav/ CoolEdit Fader/ Cross-Fader
The purpose of this module is to provide a way to apply fades to uncompressed Microsoft .wav files. Not being a c programmer, the fades are done completely in perl, making a minutes fade on a stereo 44.1 Khz, 16bit file take a considerable amount of time. The primary reason I wrote this module was because I needed a programmatic way to mix songs together for subsequent burning to a CDR. After spending many hours watching countdowns while my perl loop faded files in & out I contacted Syntrillium, makers of the excellent multitrack sound editor 'Cooledit Pro' asking for details of their file format, so I could have the perl program read the attributes of each .wav file, sort them by tempo, arrange the fading curves and write all this to a small Cooledit 'session' file for subsequent preview/ tweaking. I personally use the Cooledit mode for a number of reasons;
* You can listen to the results in minutes rather than hours.
* You can view all the waveforms together and visually see the non-destructive fades that will be applied
* It handles clipping (when the digital volume becomes larger than the bit size will allow), my program just warns you when it happens and does nothing about it :-(
Among the reasons I have left the perl .wav mixing routines is for people who may be using a non mswin32 platform or cannot justify the price of Cooledit. Also I'm kind of hoping that a c whizz will become interested and contact me about writing a super cool c mixing engine in this curious XS thing I've been hearing so much about :-) While on the subject of different platforms, I pretty sure that this version will not work on big endian processors as I'm not doing anything about network orders etc yet, as it started to make my head hurt! (Audio::Tools::ByteOrder)
Why?
The concept behind this module is that each .wav file can be marked up to give the arrangement decider (for want of a better name) clues as to the best way to mix a song into the final output. You can start out marking up the actual file with cuepoints and at a later stage when tweaking the mix you can place a hint file in a given directory and these settings will take precedence over the settings marked up in the .wav file. I'm planning to add a feature that will encode the information in the hint file into the .wav file. This should be able to be done fairly quickly as this information usually resides after the sound data block.
The Cross Fader is given either an input directory that it collects its .wav files from or a list of fully qualified paths.
The two methods for marking up files are;
Markup Methods
Cuepoints within the .wav file.
Markups should be entered with the command in the name field & the option in the description field. I've only used cooledit to mark these files so I'm not sure how the program would behave with cuepoints created in another audio editing program.
To edit cuepoints (in cooledit) choose
View -> Cue Edit* type the command in the Name & the option in Description.
Within a .wav file, Cooledit uses the CUE block to define offsets for each cue, but it uses LIST block to store the name & description information. This LIST block type is known as an Associated Data List (adtl). This method of encoding cue point names & descriptions is not universally accepted as a good thing, but I couldn't find an alternative method.
Entries in a hint file.
If a correspondingly named .hint file exists in the hints directory then this information will be used in preference to the markups within the .wav file. You can set the hint directory to be the same as the .wav input directory but this has little use when dealing with read only sources (such as CDR).
The hint file should have each command on a separate line with the option on the same line after a tab. All times should be in sample format, offset from 0 (being the start of the file).
Hints can also exist in the .wav input directory, but if this is the case they have lower priority than the ones in the hint directory.
Markup Types.
Start/ End Points
command: start/ end
options: none
These markers determine at which point the song will start/ end. Fades are started/ finished from these points
Significant points
command: sig
options: first/ last
A significant point in a song will be used as the position the next/ previous song aligns it's first/ last point to. In general it's good practice to try and make these points sit at the first beat of the bar (or at least on a beat). In this way even if two songs tempos do not match exactly at the significant point for each song it should fall on the same beat. I've found that significant points sound good at the centre of a fade in/ out
Fades
command: fade_in/ fade_out
options: linear/ trig/ invtrig/ exp/ invexp
Currently the module only supports a fade in from either the start of the file or from a start tag or a fade out to the end of the file or a end tag.
The different fade types are;
* linear - Smooth linear fade
* trig/ invtrig - Trigonomic fade. My favourite. looks suspiciously like a quarter of a circle. Inv is the inverse, i.e. starts slowly, gets louder/ quiter the nearer the end it gets
* exp/ invexp - Exponential fade. An extreme fade that follows x squared. Gets loud/ quite quickly and finishes slowly. invexp as above
AUTHOR
Nick Peskett - nick@soup.demon.co.uk
SEE ALSO
METHODS
new
Returns a blessed Audio::Mix object.
my $settings = {
'out_dir' => '.',
'fade_time' => 15,
'default_fade' => 'linear',
'hints' => {
'dir' => '.',
'mode' => 'write',
},
};
my $wav = Audio::Mix -> new( $settings );Where; (all are optional)
out_dir => the directory the mix will be created in.
fade_time => the default length of a fade in seconds.
default_fade => the default fade type
auto_fade => if this is true (1) then unmarked-up file will have the default fade applied for the default length. The significant point will be in the centre.
hints => a reference to a hash containing;
{
dir => path to read hints from
mode => read, write or blank for neither
}mix
Creates a mix of a number of given files.
my $xfade = {
'out_type' => 'cooledit',
'read_dir' => './t',
'out_file' => 'xfade',
'dao_file' => 1,
};
$wav -> mix( $xfade );Where; (* are optional) - You should have either read_dir or read_files
out_type* => either cooledit or wav (so far).
read_dir* => a directory where the source wav files can be found.
read_files* => a reference to an array of full paths to source wav files.
out_file* => the filename to write to (without extension), defaults to 'mix'.
dao_file* => 1 to write a Goldenhawk cue file (see Audio::Tools::Time).