Zend certified PHP/Magento developer

Why does a Python script only use 6 out of 12 cores?

I run Whisper on an Intel-Mac with an Intel Core i7-CPU (Whisper doesn’t seem to support AMD Radeon GPUs at the moment, hence I use CPU). When I run Whisper on this computer when it otherwise mostly is idle Whisper takes around 500-550 % CPU (1200 % is max – 6+6 cores), so around half of my CPU capacity is used. If I launch another Whisper it too takes 500-550 %, which means that my CPU is more or less fully used.

In other words, two files are processed at around half speed. I would prefer to process one file at full speed, that is, that the first Whisper process used maybe 1100 %.

Why does Python (?) only use half of the available CPU-capacity in a situation like this? Can this be controlled via some setting, flag or similar?