This explains the 3 types of each that you mentioned and then some:
http://en.wikipedia.org/wiki/Encoding_(memory)
Visual encoding is the processing of images.
Acoustic encoding is the processing of sound, particularly the sound of words.
Semantic encoding is the processing of meaning, particularly the meaning of words.
Tactile encoding is the processing of how something feels, normally through touch.
Encoding for short-term storage (STS) in the brain relies primarily on acoustic rather than semantic encoding.
Basically, each begin with a stimulus/stimuli that result in the translation of the stimulus into universal nerve impulses/signals, which get processed and encoded.
Here's a detailed explaination of how it works:
http://health.howstuffworks.com/human-memory1.htm