7.
Adding or changing Chime WAV files
Introduction
The Fortress E1T Clock uses WAV files to sound chimes and make other noises. The clock
hardware uses the two 12 bit Digital to Analogue Convertor (DAC) outputs from the SAM3X8C
each passed through Low Pass Filter (LPF) to an audio amplifier feeding a small speaker.
Input WAV file requirements
The input file requirements are:
•
•
Sample rate not higher than 44100Hz
•
Uncompressed
•
Up to 32 bit format (not 64 bit)
•
DOS 8.3 file naming i.e. no long filenames
The input file can be:
•
8 bit unsigned, or
•
16 bit signed
•
mono or stereo
Converting other formats
As long as another format file, such as a MP3, can be converted to a WAV format file then it
should be possible to use it. For file conversion I recommend the free Audacity software. Using
this software you can export the file as a WAV format readable by the Fortress E1T Clock. It also
enable you to play and edit the file. You can blend several files together and add effects like echo
and reverb. Have fun!
Copying the WAV file to the SD card
All WAV files must be copied to the WAV folder in the root directory of the SD Card. You can
access the SD card using the methods described in section 6 of this chapter.
Pre-processing the WAV files for use
The Fortress E1T Clock does not use the WAV file directly while playing a chime or sound effect.
Instead a preprocessor first converts the WAV file into a format that is directly compatible with the
DAC requirements:
•
Unsigned 8 bit data is converted to signed 12 bit data
•
Signed 16 bit data is converted to signed 12 bit data
•
Mono data is saved as two identical stereo channels
•
Channel tags are added that direct the left data stream to DAC0 and the right data stream
to DAC1
https://en.wikipedia.org/wiki/WAV
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