Small high-speed desktop cassette duplicators like this Telex Copyette 1 & 3 duplicated from a master cassette tape onto three blank cassettes simultaneously. They were popular with small studios, churches, schools and businesses. Most were monaural like this one, but a few were stereo. Frequency response was only 50 - 10,000 Hz and signal-to-noise ratio was only -45 dB or -50 dB, so they were more suited to spoken word tapes and not music. I still have a Wollensak unit similar to this one.