 After Mellotronics had targeted them as a potential customer , the BBC Radiophonic Workshop became interested in the possibilities of the instrument , hoping it would allow them to increase throughput . The corporation used two custom @-@ made models that employed recorded sound effects throughout 1963 and 1964 , but had problems with fluctuating tape speed and found the sound wasn 't up to professional broadcast quality . The Mellotron was eventually dropped in favour of electronic oscillators and synthesizers . 
