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From: nathan@visi.com (Nathan Mates)
Newsgroups: comp.sys.apple2,comp.answers,news.answers
Approved: news-answers-request@MIT.EDU
Followup-To: comp.sys.apple2
Subject: Apple II Sound & Music Frequently Asked Questions (FAQ)
Archive-name: apple2/soundmusic
Posting-Frequency: monthly
Last-modified: November 3 1997
Version: 1.7
URL: http://www.visi.com/~nathan/a2/faq/snd.mus.html
Apple II Sound & Music FAQ
Archive-name: apple2/soundmusic
Posting-Frequency: monthly
Version: Version 1.7 (3-NOV-97).
Written by Ian Schmidt (irsman@iag.net)
Thanks for corrections and updates to Michael Mahon, Joe Walters, Dave
Lyons, Dave Huang, Mitchell Spector, and Scott Gentry.
Send additional questions/comments/blatent error reports to
irsman@iag.net.
A quickie what's new:
* Added and fixed some info.
* Added the 3D sound section.
Table of Contents:
* An introduction to music and sound
* 8-bit music and sound
* Types of sound files used on the IIgs
* How to digitize sounds
* How to edit sounds
* Types of music files
* An overview of SoundSmith-style editors
* An overview of MIDI
* Technical specifications for the IIgs Ensoniq chip
* About IIgs stereo cards
* What about them other machines? And video games?
* What's this I hear about 3D sound?
_________________________________________________________________
An introduction to music and sound on computers.
Music and sound have been a computerized pursuit since at least the
1960s, when enterprising hackers discovered that by programming the
large mainframes of the time to do different operations, different
tones could be generated on a common AM radio from the interference
(this is still a problem today :-).
Early synthesizers developed at the time (known as Mellotrons)
consisted of a huge bank of tape loops, with each key playing a
different tape. Primitive analog tone generators were also in use.
These early synthesizers first got wide industry exposure via Walter
aka Wendy (never mind) Carlos' "Switched-On Bach" album. At this time
(mid to late 60s), Robert Moog developed the direct ancestors of
today's synthesizer. Moog's synthesizers were programmed via 'patch
bays', wherein the user would connect a series of jacks in a specific
configuration via patch cords to get a certain tone. This use of the
word 'patch' for a sound setting on a synthesizer persists, despite
that today a 'patch' is usually a data file stored on disk or in ROM.
The Moog's debut in a Top 40 song was Del Shannon's "Runaway". A Moog
was used along with a tube-based analog synthesizer called a theremin
in the Beach Boys' classic "Good Vibrations". The possibilities of
synthesizers weren't really exploited until the onslaught of 70s
'art-rock' bands such as the Who, Supertramp, ELP (Emerson, Lake, and
Palmer), Genesis, Yes, Pink Floyd and Rush. Synthesizers have
continued to advance to the point where they are now the only
instrument needed to make a typical Top 40 or rap album. This was
foreseen somewhat by Boston, who included a "No Keyboards!" logo on
one of their early albums despite the obvious inclusion of a Hammond
organ on several songs.
Computer control of music developed somewhat later, however. Several
companies in the early 1980s had competing systems for allowing
electronic synthesizers to interface to computers and each other,
Roland's "CV-Gate" system being among the most popular. Around 1983 or
so, a group of companies developed the now ubiqitous MIDI (Musical
Instrument Digital Interface) standard. It is now very difficult to
find a synthesizer without MIDI capabilities, and all popular
computers can be interfaced to MIDI instruments, including the Apple
II.
The first development after MIDI was introduced was the "sequencer"
program, a program which allowed the recording and playback of MIDI
data streams, as well as sophisticated editing functions. This allowed
perfect playback of songs every time, as well as more advanced
functionality such as the ability to synchronize MIDI data with SMPTE
(Society of Motion Picture and Television Engineers) time code, a fact
which made it very simple to add MIDI-based music to television shows
and theatrical films and synchronize to a resolution finer than 1
frame. SMPTE and MIDI were used heavily in the production of the
soundtrack for the recent blockbuster "Jurassic Park" for example.
At about the same time as the first sequencers were arriving,
computers began to get sound chips with some semi-decent capabilities.
Machines such as the TI-99/4A and Atari 800 had chips capable of
playing at least 3 independent tones at any one time. However, the
tones were preset, usually to a square wave, which has very little
musical interest. This went to the next step when a young engineer
developed the SID sound chip for the Commodore 64 computer. The SID
chip could play 3 tones at once [plus 1 channel devoted to 'white
noise' percussive sounds], and each of the tones could be selected
from a range of several waveforms. In addition, advanced effects such
as "ring modulation" were avalible on this chip. The C=64 soon allowed
many to compose some amazing tunes, but the best was yet to come.
The engineer who designed the SID went on to join a company called
Ensoniq, where he designed the DOC (Digital Oscillator Chip) which
powered the company's now legendary Mirage synthesizer. The Mirage was
unique in that it was the first major synthesizer to offer sampling,
wherein you could digitally record any sound you wanted, from trumpets
to snare drums to water dripping, and use it as an instrument. Best of
all, the DOC chip could play up to 32 samples at any one time, making
it useful to emulate a whole orchestra with one Mirage. The DOC chip
also powered Ensoniq's ESQ-1 and SQ-80 synthesizers.
Now, to get some Apple II-ish relevance. During the design of the
Cortland (aka IIgs), Apple was planning on using a chip not unlike the
one on the Mac II series. This chip played 4 samples at once, but was
limited in it's stereo capabilities (you got 2 samples on the left,
and 2 on the right, and that's it) as well as overall flexibility
(it's limited to 1 fixed sampling rate of 22,050 Hz). Luckily, Ensoniq
sent a sample of the DOC chip to Apple, and it ended up in the hands
of a music enthusiast working on the IIgs project. This engineer
fought with management until they decided to use the DOC chip for the
IIgs. However, up until nearly the last minute, the DOC and it's 64k
of RAM were to be an extra-cost feature, which would have killed the
GS music software market dead. Luckily, price drops on components
allowed the DOC to be standard, so all IIgs owners could hear great
sound.
Back to generalized things, the next development was to combine
sampling and sequencing software on capable computers. This resulted
in the *Tracker genre on the Amiga, as well as Music Construction Set,
Music Studio, and other programs on many platforms. These programs
typically had a sequence file and a series of sample files used as
instruments, with some notable exceptions (the *Tracker series on the
Amiga had all-in-one 'modular' files, hence the name MOD).
_________________________________________________________________
8-bit music and sound
The 8-bit IIs are quite underpowered in the sound department compared
to the IIgs. However, anyone who's played Dung Beetles or Sea Dragon
knows that some pretty sophisticated stuff is still possible. The
8-bit sound normally consists simply of an ability for programs to
make the speaker click. If a program toggles the speaker very fast,
tones are generated. And using other techniques beyond the scope of
this FAQ, you can even play digitized samples on the speaker, although
the quality isn't very good unless you can somehow hook up external
speakers. You can hear for yourself with Michael Mahon's Sound Editor
2.2, which is currently available from his web page at:
http://members.aol.com/MJMahon/
There have also been a variety of sound expansion boards available for
the 8-bit IIs, but the only one to really catch on was the venerable
Mockingboard. The Mockingboard was available in several packages. The
Mockingboard "A" was the base card, which added 6-voice music and
sound synthesis to to any alotted II. The Mockingboard "B" was a
daughterboard that worked with the "A" and added speech synthesis
capabilities. The Mockingboard "C" was essentially an "A" and "B" in
one package. The later Mockingboard "D" had the same capabilities as
the "C", but attached to the Apple IIc via the serial port.
_________________________________________________________________
Types of sound files found on the IIgs
Several types of sample files are used. Here are the most common.
Name Extension FType Description
---------------------------------------------------
Raw no std. BIN Contains only raw sample data. The auxtype
is normally the sample rate divided by 51.
(See section CA for more on why this is).
ACE .ACE $CD Contains raw sample data compressed with ACE,
Apple's Tool029 sound compressor.
ASIF no std. $D8 Contains sample data plus additional data.
Notable due to its use by SoundSmith.
AIFF .AIFF $D8 Interchange format popular on the Macintosh.
Not used much on the IIgs.
HyperStudio no std. $D8 Contains raw or ACE compressed data plus
additional information.
rSound no std. $D8 Resource fork contains one or more rSound and
rResName resources. Used by HyperCard
IIgs and the Sound CDev.
_________________________________________________________________
An introduction to sampling
Sampling is conceptually simple; an incoming analog sound signal is
converted to a digital number (0-255 on the IIgs). Getting good
samples depends on a number of factors:
* Sampling rate. This is how often in samples per second the
incoming signal is actually noticed and saved. In general, you
want to have a sampling rate of twice the frequency of the highest
pitch sound you intend to sample. (The reasoning behind this is
known as the Nyquist Sampling Theorem). Compact discs sample at
44,100 Hz, which means they can accurately track signals up to
22,050 Hz, beyond the range of human hearing. Long-distance
telephone calls are sampled at 8,000 Hz, since the characteristic
part of human voices is generally from 1000-3000 Hz. If
frequencies higher than or equal to half your sampling rate exist,
they will manifest as distortion in the output sample.
* Stereo card quality and shielding (the Audio Animator makes the
best samples of any card I've tried, by far).
* Input signal level (the higher the better, except that there is a
threshold known as the 'clipping level' above which the sampler
will be unable to track the signal. Analog tape recorders do
something very similar).
Once a sample is made, it can be manipulated in a variety of ways via
mathematics. Because this processing is digital, no degradation of the
signal can occur, unlike with analog processing. Some effects which
can be done include:
* Cut and pasting parts of the sample around.
* Mixing/overlaying two samples.
* Flanger/Chorus effects.
* Amplification and deamplification.
* Echoing
* Filtering and equilization
and much more...check out a modern rack-mounted guitar digital signal
processor for all the things possible :)
To digitize a sound (I'll use AudioZap as the example, others are
similar):
* Hook everything up.
* Check the oscilloscope. The wave should be barely touching the top
and bottom of the 'scope. Any higher and the sound is clipping;
any lower and you'll get a poor quality recording. Adjustment
methods vary by card; for the Sonic Blaster card AZ can adjust it
in software. Otherwise, consult your card's manual.
* Select a recording rate (lower numbers on AZ = faster).
* Click Record and cue up your tape or CD.
* Select Ok and then start the tape or CD.
* Click the mouse and stop the tape or CD when you are done.
You've just made a sample! congratulations! Experiment...you can't
hurt anything, but may discover fun/neat things to do!
_________________________________________________________________
Some basics on editing sounds.
(This section attempts to be program-independent, but in some cases
specific refrences to AudioZap may sneak in :-)
I'll assume you now have a sound loaded up, and whatever program is
showing you a nice wave graph. Now, you can pick out portions of the
wave by simply clicking and dragging the mouse over a part of the
wave, and letting go when you have as much as you want. If you now try
to Play, you'll only hear the portion you have selected. If you need
to adjust your selection range, many programs allow you to shift or
apple-click and extend the endpoints instead of just starting over
with a new range.
Once you have an area selected, you can cut/copy/paste/clear just like
you would text in a word processor. When pasting a waveform, you
simply click once where you'd like, and select Paste. The program
inserts the previously cut or copied piece of wave and moves the wave
over to make room, just like with a word processor.
For more specific information, consult the documentation for the
program you use.
_________________________________________________________________
AE Types of music files
Name Extension FType Description
---------------------------------------------------
MCS None MUS Music Construction Set tune.
TMS .SNG BIN Music Studio song.
SS None MUS SoundSmith song.
NTMOD None INT NoiseTracker GS module
NTSNG None BIN NoiseTracker GS song.
MOD None $F4 Amiga ProTracker module ($F4 is temporary).
MIDI .MID MDI Standard MIDI file.
_________________________________________________________________
A brief overview of SoundSmith style editors.
SoundSmith (and all other MOD derived editors) use a very simplistic
way to representing music, to wit:
0 C5 1000 --- 0000
1 --- 0000 --- 0000 ... additional tracks here
2 G5 33FF G5 53FF
3 --- 0000 --- 0000
4 C5 1000 --- 0000
This is often known as a 'spreadsheet' format since there are rows and
columns much like a spreadsheet. Let's take a look at an individual
cell:
Number of cell
| Instrument number
| | Effect data
| | /|
2 G5 33FF
/\ |
|| Effect number
||
Note and octave
For this note, it's #2 of 63 in the pattern, it's a G in octave 5,
using instrument number 3, effect 3, and data FF. What effect 3
actually means depends on the tracker in question. On SoundSmith and
derivatives, it means "Set the volume to --", in this case set it to
$FF (255) which is the maximum.
Now, into a larger structure. 64 lines of cells makes up a block, or
pattern as it is sometimes called. (some Amiga and PC editors allow
blocks of varying lengths, but we won't consider those here). You can
terminate a block early with a special effect. On most trackers, an
actual effect number is used. On SoundSmith, entering the note/octave
as NXT makes that line of cells the last line played in that block.
Now that we've covered cells and blocks, we can get into the
large-scale structure of things. To make a complete song, we can give
the player a 'block list' which tells it to play a specific sequence
of blocks in a specific order. For instance, we could have it play
block 4, then block 0, then block 1, then block 2, then block 2. An
entry in the block list is known as a 'position'. MOD-derived formats
typically allow 128 positions, and 64 (MOD) or 71 (SoundSmith) blocks.
For those of you with (gasp!) other machines and more modern trackers,
you'll notice many of these trackers have a 4th column in each track.
The extra column is usually a volume level for the track, where 0
means "don't change" and all other values do - this helps to preserve
effects and make things more flexible. Also, nearly all limits
associated with the original MOD format are no longer in force -
Impulse Tracker on the PC, probably the most advanced tracker
available today, offers 64 tracks, up to 32 megabytes of samples, and
nearly unlimited blocks and positions.
A Practical Example:
Crank up MODZap 0.9 or later and a favorite tune. Set it to the
"Classic Player". Now, remember those numbers you never understood
before, off to the left of the scrolling cells? Here's what they mean,
in terms of what you just learned: *grin*
This is the # of entries in the block list > 35 --- 0000
This is the current block list entry playing > 04 --- 0000
This is the block # currently playing > 01 --- 0000
This is the current cell # in the current block > 36 A#4 0384
As you watch, the current cell # will normally (barring certain
effects) smoothly go from 00 to 63. When it hits 63, it will go to 00
again and the current block list entry number will increment by 1.
When it does, the current block number will change if needed
(remember, a block can appear multiple places in the block list).
_________________________________________________________________
An Overview of MIDI
MIDI is a specification developed to allow computers and electronic
musical instruments to communicate with each other. Physical MIDI
hookups can get rather complicated; here is a brief primer:
MIDI hookups are a lot like your stereo, in that each device has IN
and OUT ports. However, MIDI devices also have a port known as THRU,
which retransmits information from the In port (more on why this is a
Good Thing later). MIDI devices are thus connected in a modfified
daisy-chain arrangement, with the Out of the master (usually a
computer) connected to the In of Slave #1, and Slave #1's Thru
connected to Slave #2's In, and so on. The Outs of all devices go to
the In of the master.
Here is a diagram of a simple hookup:
-----------------------------------
| ---------------- |
| | ___________ | ----- |
| | | | | | | |
In In Out In Out Thru In Out Thru
Computer Synth Drum Machine
(Master) (Slave #1) (Slave #2)
MIDI is based on 16 'channels'.
Each channel is typically assigned to one specific device you have
connected in your chain. In the example above, you might have the
synth set to listen to channels 1-9, and the drum machine set to
listen to channel 10 (this is a typical assignment). With this setup,
when the computer transmits a note on channel 10, it will first go to
the IN of the synth, which will simultaneously retransmit it via it's
THRU port and notice that it doesn't want to use the data. The note
will then appear on the drum machine's IN port. The drum machine will
transmit it on it's THRU port (to which nothing is connected in the
example) and start the note. This allows flexibility; if for instance
you wanted you could connect a second drum machine with different
sounds, set it to channel 10 also, and have a unique mix :)
I will not cover MIDI recording and editing here, because there isn't
really any good MIDI software on the IIgs to cover. That's life.
_________________________________________________________________
Technical Specs for the GS Ensoniq chip
The 5503 Ensoniq Digital Oscillator Chip (DOC) contains 32 fundamental
sound-generator units, known as 'oscillators'. Each oscillator is
capable of either making an independent tone by itself, or of being
paired up cooperatively with it's neighbor in a pairing known as a
'generator'. The generator arrangement is used by most programs, for
it allows more flexibility and a thicker, lusher sound.
The DOC plays 8-bit waveforms, with the centerline at $80 (128
decimal). This format is known as "8-bit unsigned". $00 (0 decimal
too) is reserved for 'stop'. If a sample value of 0 is encountered by
a DOC oscillator, the oscillator will immediately halt and not produce
any more sound. The DOC additionally has an 8-bit volume register for
each oscillator, with a linear slope. The dynamic range of the DOC
(the 'space' between the softest and loudest sounds it can produce) is
approximately 42 dB, or about on par with an average cassette tape.
Each oscillator has it's own 16 bit frequency register, ranging from 0
to 65535. In a normal DOC configuration, each step of the frequency
register increases the play rate by 51 Hz, and computing the maximum
theoretical play rate is left as an exercise for the student.
When oscillators are paired to create generators, there are 4 possible
modes:
* Free-run: the oscillator simply plays the waveform and stops. No
interaction with it's 'twin' occurs.
* Swap: Only one oscillator of the pair is active at a time. When
one stops, the other immediately starts.
* Loop: The oscillator simply plays the waveform and if it hits the
end without encounter.cgiing a zero, it starts over at the
beginning.
* Sync/AM: This actually has 2 possible effects: either one
oscillator of the pair modulates the volume of the other with the
waveform it's playing, or both oscillators sync up perfectly,
causing a louder and more 'solid' sound.
Oscillators play waves stored in up to 128k of DRAM. This DRAM is not
directly visible from the GS's 65816 CPU, but can be accessed (slowly)
via services supplied by the Sound GLU chip. Note that no widely
manufactured IIgs motherboard supported the full 128k of DRAM that the
DOC can see. Conversely, no synthesizer Ensoniq made using the DOC had
anything less than the full 128k.
The output of an oscillator can be directed to any one of 16 possible
channels. Apple only makes 8 channels avalible via the 3 bits on the
sound expansion connector, and all current stereo cards limit this to
1 bit, or two channels. However, the "Bernie II The Rescue" IIgs
emulator for the Power Mac expands this support to 4 discrete output
channels, two of which are encoded to the rear channel for Dolby
Pro-Logic compatible output. No IIgs software that I'm aware of
supports more than 2 channels however.
_________________________________________________________________
About IIgs Stereo Cards
Mfr Name Notes
--- ---- -----
MDIdeas SuperSonic First IIgs stereo card. Not very well
constructed, but sounds nice. Digitizer
option pretty good.
MDIdeas Digitizer Pro Daughterboard for SuperSonic, but also takes
up another slot in your GS. Pretty good, but
very few were sold.
Applied GStereo I've never used one; anyone?
Ingenuity
Applied FutureSound Most advanced card made. Includes
Visions sophisticated noise reduction, coprocessor, and
timing generator for ultimate control of
sampling rates.
Applied Sonic Blaster Generally poor to average card; boneheaded
Engineering decision to use non-shielded ribbon cable
results in hissier than average output and
digitizing.
Applied Audio Animator The one they got right. Has digitizing
Engineering circuitry external to the GS itself to avoid
noise, plus a MIDI interface.
Econ Tech. SoundMeister Generally above average quality. Nothing much
to say. Pro version with direct-to-harddisk
recording cancelled.
_________________________________________________________________
What about them other machines?
Here's a rundown of sound on other computers...
Computer or Card Wavetable voices WT bits FM voices Stereo? Digitize?
-----------------------------------------------------------------------------
Apple IIgs 32 8 None Yes(4) Yes 8 bit
Soundblaster 1 8 11 No Yes 8(4)
Soundblaster Pro 2 8 20 Yes Yes 8
Soundblaster 16 2 16 20 Yes Yes 16 bit
Soundblaster 16 AWE32/64 32 16 20 Yes Yes 16
Pro Audio Spectrum 16 2 16 20 Yes Yes 16
Gravis UltraSound 32 8/16 None(2) Yes Yes 16(4)
Gravis UltraSound Max 32 8/16 None(2) Yes Yes 16
Gravis UltraSound PnP 32 8/16 None(2) Yes Yes 16(11)
Logitech SoundMan Wave 20 16 22 Yes Yes 16
Commodore Amiga (all) 4 8 None Yes Yes 8(4)
Mac (non AV, 0x0) 4 8 None Yes(3) Yes 8(4)
AV 0x0 Mac Infinite(1) 8/16(10) Infinite(1) Yes Yes 16
PowerPC Mac 2 16 None Yes Yes 16
AV PowerPC Mac Infinite(9) 8/16(10) Infinite(9) Yes Yes 16
Game Machine Wavetable voices WT bits FM voices Other voices Stereo?
------------------------------------------------------------------------------
Atari 2600 0 0 0 2 No
Intellivision 0 0 0 4(8) No
Nintendo Ent. System 1(5) 8 5 1 No
Sega Genesis 1(5) 8 6 0 Yes
Sega CD 11(7) 8/16(7) 6 0 Yes
Super NES 8 12(6) 0 0 Yes
Sony PlayStation 24 16(6) 0 0 Yes
Sega Saturn 32(12) 8/16 32(12) 0 Yes
Nintendo 64 Infinite(13) 8/16 Infinite(13) 0 Yes
Notes:
"Wavetable" as used here means "a channel capable of playing back a
digitized waveform". This is NOT the generally musically accepted
meaning of the term, but it IS how it is commonly used when referring
to computer sound boards.
"8/16" for WT playback bits means the chip is capable of directly
processing 8-bit or 16-bit samples without conversion (the GUS's GF1
chip and the AV Mac's DSP chip obviously fit these criteria).
1 - The AV Mac's DSP chip can theoretically mix an infinite number of
wavetable voices or synthesize an infinite number of FM voices.
However, this is limited in practice by the speed of the chip and any
other things you have it doing (voice recognition, modem replacement,
etc).
2- The Gravis UltraSound can emulate FM synthesis in software.
3- Macs before the Mac II were mono-only.
4- This requires additional hardware.
5- The Genesis and NES's wavetable channel is pretty hackish, and not
very high quality; nonetheless it works for speech.
6- The SNES and PSX sound chips accept 16 bit samples which have been
ADPCM 4:1 compressed (this is similar to the ACE compression toolset
on the GS, but the data format is NOT the same).
7- The Sega CD has two channels of 44.1khz stereo 16-bit CD audio and
8 8-bit DAC channels in addition to the capabilities of the Genesis.
8- The Intellivision uses the General Instruments AY-3-8192 chip found
on Apple II boards such as the Phasor and Mockingboard. This provides
three tones and one percussive noise at once.
9- The PowerPC AV Macs have no dedicated DSP chip; they use the main
CPU, which can cause application performance degradation (see also
note 1).
10- AV Macs of both CPU types have a 2-channel 16-bit CODEC to
actually reproduce the audio, but the DSP or 60x chip are capable of
conversion.
11- The Gravis UltraSound PnP specs also apply to other AMD
InterWave-chip based boards such as the Reveal WavExtreme 32. 12- The
Saturn's 32 voices can each be set to either waveform playback or FM.
FM is not limited to sine waves as on older chips, however. 13- Like
AV Macs, the N64 uses a DSP to mix as many sound channels as you can
devote processing time to - however, since the same DSP computes the
3D geometry you're pretty limited on how many channels you would
normally want to use.
_________________________________________________________________
What's this I hear about 3D sound?
Since stereo sound has been around since at least the 1940s, people
have been attempting since then to bring the front-to-back plane into
sound, and not just the side-to-side provided by conventional stereo.
One of the more notable attempts was made in the 1960s with the
so-called "quadraphonic" system, which actually had 4 speakers and
used special LPs with 4 distinct channels. Since this is often
impractical, and nobody wanted to go to the trouble of recording 4
channels anyway, the system faded out by the mid-to-late 1970s.
With the advent of affordable DSP power in the early 1990s, and
advanced psychoacoustic research, many new systems started to appear.
Most popular is Dolby Pro Logic, which encodes 4 channels of sound
into the 2 stereo channels commonly found in stereo VHS tapes and
compact discs. This system uses 5 channels - left, center, and right
in front plus left and right rear, which are actually the same sound.
This system doesn't provide very good sound localization because the 2
rear speakers cannot play different material, and neither they nor the
center channel can play full-range sound. Nonetheless, because the
encoding for this system is cheap and easy to do, a wide variety of PC
and Macintosh software now offers it in either licensed or unlicsensed
form.
This system is being gradually phased out in favor of Dolby Digital,
or AC-3, which encodes "5.1" distinct full channels of sound - 1
channel for each of the same 5 speakers used in the older Pro Logic
plus a ".1" channel which contains only deep bass and is intended to
drive a subwoofer. This provides a very compelling sound field when
properly implemented with good quality speakers, since all 5 main
speakers can play independant full-range sounds.
There are also a variety of methods which claim to reproduce an entire
sound field with only 2 speakers or normal stereo headphones. The most
popular of these is "QSound", which has the added advantage of also
being compatible with Pro Logic, so you can get 'real' multi-plane
sound if you've got it and a reasonable imitation otherwise. QSound
was first commercially used for Madonna's "Immaculate Collection"
album, and is now used in arcade, console, and PC-based video games as
well as many other places.
Note that although Pro Logic encoding is possible in realtime on the
IIgs, no known software actually does this. Additionally, the
psychoacoustic methods such as QSound simply require too much DSP
power to pull off in realtime on the IIgs or other Apple II computers,
so be wary of any claims of such. It's certainly possible to
pre-process waveforms with QSound and simulate realtime encoding -
this method is used on systems such as the Sony Playstation which
don't have spare DSP capacity. This "cheat" may or may not work with
other psychoacoustic systems - it depends on the specific coding
method. As always, let your ears be your guide...
_________________________________________________________________
Copyright (c) 1993-1997 Ian Schmidt. Contents may be freely
distributed as long as no editing occurs without permission, and no
money is exchanged. Exceptions are hereby explicitly provided for Joe
Kohn's Shareware Solutions II, the services GEnie and Delphi, for the
current Apple II FAQ maintainer (Nathan Mates), and for user groups
everywhere.
The Apple II: It just keeps going and going and going....