Audio is one of the four accessible formats that may be used by people with a print disability.
According to the National Center on Accessible Educational Materials 
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The audio format renders content as speech to which the student listens. In Maine we refer to audio format as materials recorded with human speech (as opposed to machine-generate, synthesized speech). If the audio format is created in a flexible way — for example aligned to NIMAS or DAISY standards — there are many ways in which the speech output can be adjusted. Depending on the technology used, changes in the pitch, volume and speed at which the speech is presented can be made. Other features in audio files such as navigation are extremely important so that the user can go forward and backwards, and jump to page numbers, chapters, titles etc.
Students who are blind or visually impaired, who have difficulty with reading text, or who spend a great deal of time trying to decode text may benefit from the use of auditory text. When content is presented auditorily it can reduce the cognitive load of trying to read text or braille and can focus on comprehension of the information. Decisions are made based on a student’s needs, the environments in which tasks will be completed, and the nature of tasks the student needs to accomplish. For example, students who use braille may prefer using the audio format in different settings where they cannot easily use braille books or have technology available to use refreshable braille, text-to-speech, or enlarged text on a computer screen. Human speech may be a personal preference or it may be preferred for specific subject matter such as Shakespeare, math, science or other technical content.