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CU Amiga Magazine's Super CD-ROM 20 (1998)(EMAP Images)(GB)[!][issue 1998-03].iso
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1995-04-01
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4KB
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129 lines
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| //
| \X/ Flowerpower *proudly* presents
|
-----+------------------------------------------------------------------------
|
| a 14 Bit low level sound driver for CyberSound audio sub system
|
EMAIL: flowerp@eikon.e-technik.tu-muenchen.de
INTRODUCTION
------------
This is a driver to replay a 16 bit Stereo audio stream via the Amiga audio
channels in 14 bit quality. It will adapt to different screenmodes,
allowing up to 60khz output frequency on AGA machines and about 28khz on
ECS machines. For maximum sound quality, the driver can be calibrated
using a prefs program. The core routines are written in assembly for
maximum speed, but optimizations are always possible.
HARDWARE/SOFTWARE REQUIREMENTS
------------------------------
An Amiga with at least Kickstart 2.0 and a MC68020 processor should
suffice. The driver takes approximately 150kb of memory, mainly for
tables. Chip memory usage is neglectable as this driver uses very small
buffers and is heavily interrupt driven.
CALIBRATION
-----------
Calibration of the driver will decrease the noise level and improve the
sound quality. Every Amiga has got a different characteristics in its D/A
converters. They are not exactly linear. The calibration program allows
you to measure out the step sizes of the D/A converter. So the 14 bit
driver can create an optimal conversion table.
Calibration will take approximately 20 minutes. If you want to do it very
exactly you may invest 2 hours as well ;-)
The program will explain itself. Please follow the instructions of the
program in order not to damage your HIFI equipment.
THEORY OF OPERATION
-------------------
14 bit output is created by mixing a channel at maximum volume with a
channel playing at minimum volume. As this is done on the left and on the
right side, it takes all 4 audio channels.
PROGRAMMER'S DOCUMENTATION
--------------------------
This is not yet available, as this driver is not yet finished. The
software interface may change at any time. If you are interested in how it
works, look into the source code of the CDPlayer program.
In the future the cybersound.library will be responsible for creating the
audio stream, so direct programming of this driver will be useless.
Currently the driver is limited to LITTLE ENDIAN audio streams as created
by the Toshiba CDRoms. As this is not the best stream format for realtime
mixing on the Amiga, a stream format selection will probably be included.
The source code is included for "educational" purposes only.
FUTURE ENHANCEMENTS
-------------------
* miscellaneous changes in the software interface
* further optimizations for special stream formats
* program a Toccata and Maestro driver as well
PROGRAM HISTORY
---------------
Sounddriver 1.1
* The audio hardware was reset even when the driver failed to open. This
could disturb other programs, e.g. module players. Fixed.
* The audio stream format is now selectable. The application can switch
between big and little endian. The CDPlayer uses little endian because
the CDRom delivers that data format. A library like cybersound.library
would of course use big endian (motorola format).
Calibration 1.1
* Fixed some enforcer hits that occured when saving the configuration. You
really shouldn't peek into a menu structure that has already been
deallocated. ;-)
CONTACT ADDRESS
---------------
EMAIL: flowerp@eikon.e-technik.tu-muenchen.de
FidoNet: 2:2480/465
SnailMail:
Christian Buchner
Ganghoferstraße 2
82110 Germering
Germany
Tel.: +49-(0)89/844872