Learners beware: the pronunciation of "ch"
I noticed that the computer voice pronounces the "ch" in the word "mochila" as a very hard "tch." Even though this can be one of many regional or allophonic variants, I just wanted to let everybody know that you do not need to closely reproduce this sound. The Spanish "ch" basically equates to just one sound, and it will be well understood most of the time regardless of whether you pronounce it as "tch" or "sh" or anything in between. As with most Spanish sounds, trying to find a middle ground is generally the best course of action. For different pronunciations of "mochila", check this out: http://www.forvo.com/word/mochila/#es