Audio Systems: Cassette recorder, variable speed motor, razor blade

Question

As the capstan on the recorder turns and unwinds the tape on the feed reel, the
circumference of the tape on the reel will become smaller which would appear to cause
the tape passing the head to  become slower. Does the recorder have a constant speed
motor and is the decrease in linear tape speed across the head accounted for in the
recording as the tape passes the electromagnet in the head OR does the unit have a
variable pseed motor and, if so, how is the speed controlled?  

Answer
Felix-

All tape I've worked with is pulled at a steady rate. Variable speed motors would be very difficult to sync up, and unless they were made to a very high standard, would make the recording sound warbled. Also, a variable speed motor would make splicing an existing recording impossible, since, if it were recorded with some sort of compensation for a varied speed, adding or deleting material with a razor blade would change the position of the material on the tape, throwing the entire recording out of whack. As far as I know, the visible decrease in speed is nothing more than an optical illusion.


-Steven L Smith