Pierre Parenteau (the developer) told us what is under the hood: “To keep the plugin light, each sound contains only one sample stretched over the keyboard. The C3 note has been sampled for each sound, but in some cases you’ll hear a different note (C1 or C2)”. Also, to respect the original mapping of the PSR-78, he decided to keep the C1 and C2 notes to C3. In the zipped download file you will also find the WAV files which stay at the core of the instrument (labeled and looped).
Toy Keyboard is a free VST/AU plugin instrument for Windows (32- & 64-bit VST) and Mac OS X (64-bit VST/AU). It is available for free/donationware (in case you want to contribute with any amount and encourage the author to keep up the good work).
The download size is 173MB (comes with all installers for Windows and Mac OS X plus the instrument and drum/percussion samples). A valid email address is required for the download link.
Download Link
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 WIN/MAC FREE){kind=link}