Open system compact cassette (OSCC) documentation
This wiki contains the documentation for the open system compact cassette (OSCC) project and its components.
Planned playback modes
This project aims to improve cassette playback on drives that are equipped with OSCC hardware and software. The following playback modes are planned:
Common analog mode
This is the common playback mode on ordinary cassette hardware with a little improvement: A microcontroller regulates the motor speed. The microcontroller detects speed variations that can occur for example when a tape is hard to pull and increases/decreases the PWM duty cycle for the motor's energy supply to keept the correct playback speed.
Enhanced analog mode
In this mode, a tracking signal with a frequency of 19kHz and an amplitude of 80% is recorded onto the tape. On playback, that signal is detected by a microcontroller which alters the motor speed so that the signal is played back at a frequency as close as possible to 19kHz. The microcontroller shall also react quickly on speed variations by altering the motor speed when the frequency of the tracking signal deviates from 19kHz. Depending on how fast the microcontroller can alter the motor speed, this might reduce wow and flutter a lot, even with faulty belts.
The digital mode stores data or digital audio on the cassette. When playing back digital audio, the motor speed is controlled by a microcontroller to match the bitrate of the stream so that there is neither buffer underrun or buffer overrun in another microcontroller that decodes the audio data. This means that the tape speed can be very low on highly compressed voice recordings so that hours of digital voice recordings could fit on one cassete.
OSCC cassette drive architecture
An OSCC drive is composed of the following components:
- A Motor unit that controls the motor speed.
- A Drive unit that controls drive mechanics and sends signals caused by mechanical parts.
- A Control unit that handles user input (pressing buttons) and controls the motor unit and the drive unit.
- A Signal processing unit that reads data/information from a tape and may possibly write data/information onto it.