What would be considered to be a fast dictation/audio?

The average conversion ratio of audio to text is 1:10; i.e. for one minute of audio you get 10 lines of text. One line of text is calculated as 65 characters inclusive of spaces. Hence, if the conversion ratio goes above the 1:10 ratio, the dictation/audio would be considered to be a fast dictation/audio. However, we do give a leeway of up to 12 lines per audio minute. Only dictation/audios having more than 12 lines per minute of dictation/audio will be deemed to fall under difficult audio category.