The Mockingboard PSGs base their frequency on the Apple II Clock.
https://groups.google.com/g/comp.sys.apple2/c/lNSdI9GyBgc/m/8tAydOPUAwAJ
Based on this discussion I made a spreadsheet to calculate the correct values of the frequency tables and updated the ones used by the Music Construction Set player.
The MCS-CRICKET player set the VBL as an interrupt source using the
mouse firmware. This had several limitations, since it is only
available on the //c but also because depending if the //c is a PAL or
NTSC model it would produce a 50Hz or a 60Hz interrupt.
This version uses the ACIA as an interrupt source instead making it
also compatible with other Apple II models with a Super Serial Card.
The interrupts are caused by a Cricket alarm set to 60Hz making it
region independent as well.
The Street Electronics ECHO+ sound card complemented the popular ECHO
speech card with two AY8913 providing similar sound capabilities to
those offered by the Mockingboard.
A very clever design allowed it to use only one 6522 instead of two but
also made it incompatible with the few titles to ever support
Mockingboard sound, making it even less popular.
This routine considers the slight differences between both making it
possible to play music on this rare card.
A slot number different that slot 4 can be used for the Mockingboard.
A separate simple player introduced to include the minimum amount of
code required for the routine to work.
