The use of text has over powered hard copy material over the years. Most people prefer text over books because they are cheap and can easily be updated. Changing the text in an audiobook or e-file does not require that much technological knowhow but changing the words in a voice over would require you to record a new file, use special audio tools and level the sounds and programme to match the original audio file. E-learning allows you to work on your skills and spend as a learner. Most skilful readers will remember and optimise their speed through e-learning. It allows you to repeat, reflect skip, and pause in order to digest a material. Why is audio essential in the digital world? People who are trying to learn a new language sometimes need to hear pronunciation before they can learn the word. The closest some people can get to this is learning through the TTS. Doctors use them to listen to the heart murmur and call centres have replaced humans with text to speech to respond to customers among other reasons.
Do texts and audios work well together? Keep in mind that even though the audio may be all on words it is not just a sentence read out loud. Look at it this way; even though you listen to the audio through your ears, the text is received with the eyes. The two are processed separately by your brain. They both complement each other instead of competing with each other when it comes to the TTS. Learning from the text and audio separately yields more results than learning from both simultaneously. If used together, they have the ability to overrun your sound channels and sight. If the TTS is reading at a faster speed you will have a difficult time catching up. An audio alone will yield a better performance and even better when some graphics or pictures are involved.