NOTE: Original source site has gone down - a mirrored version exists at this location
Information and software from (http://dxforth.netbay.com.au/#kcs) where it was listed under the following license:
"Disclaimer: The projects presented here are experimental in nature. They may be incomplete, not fully tested or contain defects. Being free software, it is provided 'as is' and without any warranty. Use of these projects or information is strictly at your own risk and responsibility. Project material written and created by the author is Public Domain; any non-original or reference material included may be subject to copyright by their respective owners."
KCS - A Kansas City Standard/CUTS Tape Conversion Utility
This is for all you old-timers that still have computer programs on cassette!
One of the most popular early ways to store computer programs on audio cassettes was the Kansas City Standard (also known as the 'BYTE standard'). Developed in 1975, it uses an encoding scheme where a '0' bit is represented as 4 cycles of 1200Hz and a '1' bit as 8 cycles of 2400Hz. The data rate is 300 bits per second. Computers which used the Kansas City Standard include S100-based systems, PT SOL-20, Ohio Scientific C1P/Superboard II, Compukit UK101, Acorn ATOM and many others.
The "KCS" utility allows programs stored on cassette tape using either the "Kansas City Standard" or "CUTS" (Processor Technology Computer Users Tape Standard) to be decoded to a program file. The reverse process - converting a program file to an audio wavefile is also possible, allowing one to produce perfectly regenerated cassettes. KCS works with 8-bit mono WAV, VOC or RAW audio files recorded at 22050 samples per second. A variety of serial formats are allowed including 7 or 8 bit data, 1 or 2 stop bits, odd/even or no parity.
NOTES
- Decoding
a) The audio file MUST be an 8-bit mono file recorded at 22050 samples per second. Any other format will result in failure.
b) Though the decoder will handle a wide range of input levels, it is best to sample the audio source at moderate to high levels. Slight clipping should not cause any problems.
c) It is not necessary to specify the number of stop bits when decoding - unless the strict option (-X) has been selected.
d) Decoding begins with the start bit found and continues until the end of the file or an error occurs. If there is more than one program present on a wavefile, the programs will be concatenated. The output file will contain program data in the form found on the tape. It may be viewed using the -C switch if desired.
e) If an ill-formed bit is encountered, a "Bad pattern" error will be displayed. Any preceding valid data will be saved before the program exits. Pattern errors may result from a variety of causes e.g.
- not 8-bit mono wavefile recorded at 22050 samples/sec.
- not Kansas City Standard or CUTS data
- serial format not correct (default settings allow either
8N1 or 8N2 data to be decoded).
- incorrect baud rate (default 300)
- very low recording level
- wavefile has very poor waveshape, excessive DC offset or
phase shift
f) DC offset, hysteresis and timing controls (-F -H -G)
Wavefiles having a very poor waveshape may give rise to
"bad pattern" errors. This can be due to head mis-
alignment between the cassette record and playback
devices. Such problems can sometimes be compensated for
by the judicious use of the DC offset and hysteresis
controls (-F -H). The default values are 0 and 3
respectively.
Speed difference between tape record and playback devices
can also result in decoding failure. The timing control
(-G) can be used to compensate. The default value is 0.
g) Playback device
If the tape playback device has any tone controls, these
should be set for a 'flat' frequency response.
Avoid portable cassette recorders of the "ghetto blaster"
variety as these often have bass and treble boost which
can introduce excessive phase shift and affect decoding.
Experimenting with the tone or treble controls may help.
A hi-fi stereo cassette deck should work well, but sample
from one channel only.
- Encoding
a) When encoding, it is important to specify the correct number of stop bits otherwise the machine on which you wish to use the tape may have problems reading the data!
b) The default tone used is a shaped square wave and results in an optimum waveform when played back from a cassette. A sine wave option is provided (-T switch) however it is likely to be less effective, particularly at the higher baud rates.
c) It should not be necessary to use the waveform invert option (-I switch). Most computers should handle waveforms of either polarity.
d) The encoded wavefile can be stored very effectively using any file archiving program such as PKZIP, ARJ, WinZIP etc. Archived wavefiles are typically 1% of their original size.
-
Baud rates higher than 300
The Kansas City Standard specifies an operating speed of 300 baud. A common modification by users was to increase the speed to 600 baud or higher. This was achieved by either doubling the tone frequency or halving the cycles per bit.
The KCS utility can only decode/encode higher baud rates which use the latter method.
-
CUTS format
The CUTS format was created by Processor Technology Corp. and was meant to be "upward compatible" with the Kansas City Standard. Many Processor Technology program tapes were recorded using 300 baud Kansas City Standard on one side and 1200 baud CUTS on the other.
Technically, the CUTS format is similar to the Kansas City Standard but uses a 1/2 cycle of 600 Hz to represent a '0' bit and 1 cycle of 1200Hz to represent a '1' bit. The data rate is 1200 bits per second. The serial format is one start, 8 data, two stop bits, no parity.
An external utility SOLENT is available which will convert CUTS binary program files produced by KCS to text form suitable for loading into a PT computer or emulator.
-
Phase distortion issues
All audio cassette players include 120 uS tape equalization during replay - a side effect of which is the creation of phase distortion. While this is inaudable to the ear, it can affect computer program data. To counter this, many computer cassette interfaces included phase precompensation in the audio output.
Some computers did not include phase precompensation. The reason why this did not adversely affect performance was either 1) very low baud rate or 2) a phase-locked loop was used for decoding which is relatively insensitive to phase distortion anyway.
A wavefile with phase distortion can sometimes be corrected sufficiently to allow decoding with KCS. To do this you need a wavefile editor that can apply low-pass or high-pass filtering (which one works will need to be determined by experiment). The filter frequency should be set to approx 1KHz with a 6dB per octave roll-off.
Note: The wavefiles produced by KCS are precompensated (square wave only) and therefore suitable for recording to cassette.
-
Minidisc, MP3 and other "lossy" audio formats
These formats were intended for music and voice use only. Do not use them to compress or store computer data wavefiles! They use lossy compression methods which can introduce enough distortion to make subsequent decoding of program data impossible.
Note: Wavefiles produced by KCS compress extremely well when archived using ZIP etc. Not only is there no loss of signal quality, the compression is far superior than that obtained by storing on Minidisc or as an MP3 wavefile.
-
Limitations
KCS is not very tolerent to phase shift distortion and there may be occasions where some tapes which work fine on your computer simply won't decode using the utility. See section 5 for further details.
-
References
The decoding algorithm is derived from that found in Wouter Ras' ATOMTAPE utility. (www.homepages.hetnet.nl/~wouterras/atom.htm)
-
History
0.4 Included Processor Technology CUTS tape format 0.5 Fixed sine tone option for CUTS mode 0.6 Re-organised interface. Many options have been changed and decoding is now the default mode. Added parity and 7 bit data options. 0.7 Decoder changed to give better results with marginal tapes. Added timing control. 0.7b Updated to DX-Forth 3.1 - no functional change 0.8 Faster decoding. Add option to ignore decode errors.
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent