Abstract: Improved speech sounds are produced from an all-software speech generating program on a computer which does not have a digital-to-analog converter by polling a first timer connected to the computer's speaker until a time-out is found, then applying a sample time value to a second timer so connected, and restarting the first timer. This results in the generation of a variable-duty-cycle carrier without interfering with the computer's operation. In an alternative embodiment, the first timer is used to generate an interrupt at regular intervals, and a sample time value from a storage buffer is then applied to the second timer.

Abstract: A copy protection system for computer discs in which a key sequence of 1101 in a copy protection section of the program is deliberately rendered ambiguous by repeatedly recording a word containing that sequence while gradually shifting the phase of the transition forming the central "1" of the sequence until the sequence becomes 1011. When this series of words is repetitively read, successive reads will be inconsistent with one another. The gradual phase shift cannot be reproduced if the disc is copied on a standard personal computer, so that the inconsistency on successive readouts will not be present in a copied disc. The program is so designed that it cannot run unless inconsistencies are detected in the copy protection section of the program. The provision of "1"s on each side of the central, variable two-bit sequence prevents spurious loss of synchronization on the copied disc which could be interpreted as an inconsistency.

Abstract: Clear speech can be produced on a DAC-less personal computer from an all-software speech-generating program with an unlimited vocabulary by applying to the computer's speaker a square-wave carrier signal of ultrasonic frequency, and varying the duty cycle of the carrier signal in accordance with digitized speech samples to produce an audio signal. The computations necessary to produce the speech samples are so timed by the program that the CPU is free to turn the speaker on and off between computations at precisely the right instant for the correct generation of a carrier having a constant ultrasonic frequency and a duty cycle determined by the value of the speech samples.