Frequently Asked Questions
How do I handle wav-files for playing the audio samples?
Some boards have an audio codec that receives the audio sample stream via the i2s-interface. Other boards have an audio output from a DAC (Digital to Analog Converter). In both cases, a stream of audio samples are output. A wav-file contains audio samples and the (uncompressed) format is simple to work with.
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- Install a PC application that can edit audio clips in the wav-format, for example WavePad Sound Editor (http://www.nch.com.au/wavepad/index.html)
- Open the audio file that you want to work with.
- Make the adjustments needed on the file, for example trim leading and trailing silent sections.
- Save the file in a suitable wav-format. First select the "Save File As" operation and then select the format. Typically 16-bit resolution and "PCM uncompressed format", mono or stereo format. Select the sample rate also.
The higher the sample rate is, the bigger the wav-file will be. If it shall be stored on the on-chip flash memory, the size is really limited (typically less than 512 kBytes).
- The wav-file contains a header with some information about the audio samples, for example bitwidth, mono/stereo and sample rate. Your player application can interpret this information and make the necessary adjustments to the player application. Alternatively, the wav-file header can be removed so that the file only contain audio data. Use for example the PSPad editor for this. Open the file in hex-mode and then it is possible to delete bytes in the beginning of the file. Normally the 44 first bytes shall be removed. Google on the wav-file format and the header for details.
- The saved wav-file (or audio sample file) must then be converted to a c-struct. There are many "binary to c" conversion programs (just google it, for example "bin2c", for example sourceforge.net/projects/bin2c).