[urubu]

Standing calf raises train the gastrocnemius and the soleus. Many gyms also have a seated calf raise machine which is meant to isolate the soleus.

I don't think I ever felt anything special after using it.

[digdugdirk]

You'd know if you had isolated the soleus. It feels weirdly (but noticeably) different to activating the gastroc. Much deeper and more centralized.