All four recorders subscribe to the 'professional' format, namely a 26.5cm diameter maximum reel capacity with at least two high speeds (19 and 38cm/sec), and a two-channel half-track format on 6.25mm (¼in) tape. However, strictly speaking they should be called 'semi-professional', as although they are essentially capable of master quality recordings, they do differ from true studio machines in several respects. For example, the input and output connections of professional machines are generally balanced-line with Cannon or similar type sockets. In contrast, the review models are all unbalanced, with phono and DIN-type inputs and outputs, plus lower line levels.