While some medical and legal transcription rates may be according to the typed line, rates for general transcription are often depending on the sound minute or audio hour - the number of recorded material in a particular audio file and those rates can change based on the kind of substance, the content as well as the industry the audio files are coming from.
For instance, some audio files may be from an individual who ordered notes for a novel or personal diary, while transcript jobs may require lots of business specific research for phrases and terms beyond regular day-to-day language. So while some transcription rates may establish their rates according to complexity and research time, others only charge a set rate no matter how sophisticated it's or what the content.
Many beginning transcriptionists establish their transcription rates at the lower end of the scale to get started in the company, subsequently raise their rates according to their level of expertise and proficiency in the field.
But whether you're establishing your rates as a company owner or you're looking to take on overflow work from a transcription business that is bigger, you need to make sure you're getting paid a decent rate without shortchanging or undercharging yourself just because you are new to the subject. You surely do not want to work just because you are new to general transcription.