Sound Manager 3.0, a vastly improved call-for-call replacement for the Sound
Manager in System 7, provides QuickTime and other sound clients with a set of new and
improved features, including higher frame rates and better quality sound. Sound
Manager 3.0 is an extension that entirely replaces the older Sound Manager; the
extension is included along with a new Sound control panel on this issue's CD. We
released it as an extension without changing the API so that you won't have to recode
your existing applications. With Sound Manager 3.0 installed in your system, your
applications will transparently take advantage of the Sound Manager's greater
dependability, speed, and other new features.
The soon-to-be-available Inside Macintosh: Sound(or Inside Macintosh Volume VI,
Chapter 22) is the main source of Sound Manager documentation. This column will
discuss some of the new features of Sound Manager 3.0 and describe how to use them.
OVERVIEW OF MAJOR NEW FEATURES
Sound Manager 3.0 provides four major new features:
Previous versions of the Sound Manager could only support stereo 8-bit audio samples
with sample rates up to 22 kHz. Sound Manager 3.0 removes this limitation by
allowing stereo 16-bit audio samples with sample rates up to 65 kHz, providing
CD-quality audio in QuickTime movies and other audio applications. Sound Manager 3.0
will also automatically convert 16-bit sounds into 8-bit sounds on Macintosh
computers that don't have 16-bit audio hardware.
Third-party sound cards can be installed in your Macintosh to allow playback and
recording of CD- quality audio. Sound Manager 3.0 makes this possible by providing a
driver mechanism and a new Sound control panel that allows the user to redirect sound
to any available audio device. Audio card developers can license the Sound Manager 3.0
extension and bundle it for distribution with their product.
The Sound Manager previously supported only MACE audio compression at ratios of 3:1
and 6:1. Sound Manager 3.0 goes beyond MACE to support any compressed audio
format with the use of plug-in audio compression/decompression software (codecs).
These are simply extension files that the Sound Manager recognizes and uses when it
needs to play a compressed sound. In this way, applications can play compressed sounds
seamlessly without being aware of the compressed format.
Sound Manager 3.0 is much faster -- in many cases two to three times more efficient
than previous versions. This means that your application can do more while sound is
playing. Sound Manager 3.0 isalso more robust: many bugs have been fixed and a
number of commonly requested features have been added.
SYSTEM REQUIREMENTS AND INSTALLATION
Sound Manager 3.0 requires the Component Manager, so you must have either System
7 with QuickTime or System 7.1. (The Component Manager comes with QuickTime and
is built into System 7.1.) Sound Manager 3.0 supports all Macintosh models except for
the "classic"-style hardware such as the Macintosh Plus, SE, and Classic.
Installing Sound Manager 3.0 consists of dragging the Sound Manager extension and the
new Sound control panel to your System Folder (where they will be placed in the
appropriate folders) and rebooting. You should see Sound Manager 3.0's icon during
startup.
WHAT'S NEW AND IMPROVED
Here are some more details about new and improved features in Sound Manager 3.0.
Speed optimizations. While Sound Manager 3.0 can play virtually any type of
sound, it has been optimized for maximum playback efficiency with a number of
common sound formats. So if you're worried about performance and want to minimize
Sound Manager overhead, use one of these sound formats:
Increased efficiency is a major improvement in Sound Manager 3.0. In many cases, the
Sound Manager will be two to three times more efficient, which allows applications to
play more simultaneous sounds and do other work while sound is playing.
For example, you can now play four channels of sound on a Macintosh LC, whereas in
the past the Sound Manager would not allow this. QuickTime applications benefit from
Sound Manager 3.0 by gaining an increase in the movie playback frame rate. The
premiere multimedia platform is now QuickTime 1.6 and Sound Manager 3.0 on a
Macintosh!
Sound quality. Sound Manager 3.0 uses a fast linear interpolation for 11 kHz to 22
kHz sample rate conversion, which makes audio sampled at 11 kHz sound much better.
This improves the sound quality of many QuickTime movies without sacrificing
performance.
16-bit sound. Sound Manager 3.0 includes full support for 16-bit audio samples,
including rate conversion, mixing, and decompression. It will automatically convert
between 16-bit and 8-bit samples, so you never have to worry about the hardware
you're running on. If your system has a 16- bit sound output device, you'll notice an
increase in sound quality.
Until now, the value of the sampleSize field of the extended or compressed sound header
has been 8 to denote the number of bits per sample. To play 16-bit sounds, specify the
value 16 for the sampleSize field in the header, and the Sound Manager will treat the
sound data as 16 bits per sample. 16-bit sounds are always in two's complement
(signed) representation while 8-bit sounds are always in offset binary (unsigned)
representation. For an example of how to fill out the extended sound header so that you
can play 16-bit sounds, see Play16BitSound on this issue's CD.
Playing compressed sounds. With Sound Manager 3.0, you can play sounds
compressed with any algorithm when you use the CmpSoundHeader data structure. The
CmpSoundHeader's old futureUse1 field is now the format field, which you can use to
specify a 4-character OSType that identifies the compression algorithm. If the
compressionID field of the CmpSoundHeader is set to the constant fixedCompression,
the Sound Manager uses the OSType in the format field to find a codec that can
decompress this type of audio. The example named PlayCompressedSound on the CD
shows how to fill out the compressed sound header so that you can play compressed
sounds.
The SndPlayDoubleBuffer call has a similar interface. It accepts a new
SndDoubleBufferHeader data structure that's identical to the previous one with the
addition of a format field at the end. If thedbhCompressionID field is set to the constant
fixedCompression, the format field is used to determine the codec to use to decompress
the sound. Otherwise it will work as before.
Multiple sound channels. The overall sound volume (amplitude) has been
improved when multiple sound channels are being mixed. In the past the Sound
Manager would average the amplitudes for all playing channels. With Sound Manager
3.0, this averaging does not occur, which gives you better individual volume control.
One possible disadvantage to this is that clipping can occur when many sounds of high
amplitude are used.
For those of you trying to synchronize multiple channels, syncCmd could never
synchronize at a fine enough level. With Sound Manager 3.0, syncCmd synchronizes
multiple channels so that independent sounds can be triggered at exactly the same time.
The technique to synchronize multiple channels remains the same as before. See the
PlayTwoSoundsSynched example on the CD.
Finding the sound header in a 'snd ' resource. The 'snd ' resource is a
cumbersome structure to parse. The old routine SetupSndHeader can be used to create
this resource. A new routine, GetSoundHeaderOffset, has been created to locate the
embedded sound header, which is used with the soundCmd or bufferCmd. The resulting
offset is the number of bytes into the handle to the starting point of the sound header.
The handle doesn't have to be locked to get this offset. See the PlaySndHandle example
on the CD.
Volume control. Two new sound commands, volumeCmd and getVolumeCmd, allow
better control of a channel's output volume. You can use volumeCmd to set the volume.
The param2 portion of the command contains a two-word value (four bytes) that
represents a pair of volume levels; the high word is the level for the right output
signal and the low word is the level for the left. A value of 0x0100 is full volume and
0x0080 is half volume. For an example of setting the volume, see ChangeVolume on the
CD.
You can overdrive the volume if you want to amplify low signals. A value of 0x0200
would be twice full volume. Furthermore, you can independently control the right and
left volumes. The value 0x01000000 would send the output signal to the right, and
0x00000100 would send it left. The value 0x00800100 would play out the right side
at half volume and the left at full volume.
The getVolumeCmd command returns the current volume. The param2 field should be a
pointer to a long, similar to getAmpCmd.
There are two new routines for controlling the volume of system beep sounds:
GetSysBeepVolume and SetSysBeepVolume.
pascal OSErr GetSysBeepVolume(long *level)
= {0x203C,0x0224,0x0018,0xA800};
pascal OSErr SetSysBeepVolume(long level)
= {0x203C,0x0228,0x0018,0xA800};
SysBeep will create a sound channel adjusted to the volume level last set by
SetSysBeepVolume. This allows for system beep sounds to play back at a lower level
than the rest of the machine, so you can hear a QuickTime movie running at full
volume but hear alert beeps at a softer level.
The older routines GetSoundVol and SetSoundVol were implemented as a Control call to
the Sound Driver. Although we've made every effort to continue supporting them, they
do not have the amount of accuracy that's available with two new Sound Manager
routines GetDefaultOutputVolume and SetDefaultOutputVolume:
pascal OSErr GetDefaultOutputVolume(long *level)
= {0x203C,0x022C,0x0018,0xA800};
pascal OSErr SetDefaultOutputVolume(long level)
= {0x203C,0x0230,0x0018,0xA800};
The older routines used a 0-7 value range whereas the new Sound Manager has a
0-0x0100 range. These new routines use the right/left volume pair as described
above for volumeCmd. Each device has its own volume level. If the user changes the
selected default device from the Sound control panel, that new device will use its own
volume level, originally set by a previous call to SetDefaultOutputVolume.
Better stereo support. Previous versions of the Sound Manager would drop the
right channel of a stereo sound when playing on monophonic hardware, such as a
Macintosh LC. Sound Manager 3.0 will automatically convert stereo sounds to mono on
these machines without dropping the right channel, so you can hear what you've been
missing. Certain older Macintosh models are also mono out of the internal speaker, but
stereo if headphones are plugged in. Sound Manager 3.0 will automatically sense if a
headphone is plugged in and do the correct conversion so that both the right and left
channels of a stereo sound will always be heard. The only exception is the Macintosh
IIfx, which requires you to manually select stereo or mono in the new Sound control
panel.
Default output device. Sound Manager 3.0 includes the concept of a default output
device, set by the user in the new Sound control panel using the Sound Out panel. All
sounds will be sent to this device unless an optional device was specified with
SndNewChannel. The default device is generally the built-in sound hardware. The user
can choose a new device (such as a sound card the user installed), and all sounds will
then be routed to the chosen device. Adjusting the volume with either the control panel
or the older call to SetSoundVol adjusts the volume of the default device.
Integration with QuickTime. QuickTime 1.6 is aware of Sound Manager 3.0 and
will take advantage of its new features if it's installed.
Sound Driver compatibility. The old Sound Driver, including the use of
SoundBase, still works with Sound Manager 3.0, but we don't know how much longer
this will be true. This depends entirely on changes in the hardware, not on the Sound
Manager. If you're currently using the Sound Driver, Apple strongly encourages you to
use the Sound Manager instead. Future changes in the sound architecture will be
transparent to your application if you use the Sound Manager; they won't be if you
continue to use the Sound Driver.
CPU loading. The Sound Manager released with system software versions 6.0.7 and
later contained support for CPU loading. This approach was found not to be very
accurate, and is not supported in Sound Manager 3.0. Sound Manager 3.0 will return
the constant 7% for any channel, no matter how it was created and initialized. The
number 7% was chosen because some applications were expecting a nonzero value, and
7% is about right for a Macintosh LC playing a single 11 kHz mono sound. Since the
Sound Manager doesn't have true CPU loading checks, it's possible to run out of real
time and thus overload the machine. Sound will then break up or even hang the system.
This problem will be addressed in a future version of the Sound Manager.
Synth modes. Previously the Sound Manager enforced a single synthesizer type to be
allocated. Even if a given synthesizer type allowed for multiple channels, you still
couldn't mix the types. For example, you couldn't use the wave table mode while any
other mode was operating. This limitation has been eliminated. Any and all three types
of channels (square, wave table, and sampled sound) can be opened and used at the same
time.
Square wave sounds. Unknown to most, the square wave synthesizer never
produced true square waves. It was more like a modified sine wave. This has been
corrected. As a result you'll notice that the Simple Beep sounds different. It can now be
heard as it was originally designed to sound.
BUG FIXES AND FEATURE ENHANCEMENTS
The following is a brief summary of bugs that have been fixed in Sound Manager 3.0.
This is not a complete list. Its intention is to point out major areas of improvement
that might affect a large number of applications.
Play from disk
Sound Input Manager
Sound Output Manager
SOUNDING OFF
Sound Manager 3.0 is a vast improvement over the old Sound Manager and will enhance
QuickTime applications and other applications that use sound. So check it out; from the
system beep to sophisticated movies, we're sure you'll notice the difference.
An important feature of Sound Manager 3.0 is the ability to play through alternate
sound output devices installed in your system. These devices will be available from
third-party developers. The Sound Manager can take advantage of specialized hardware
features such as sample rate conversion and audio mixing. If such features are
available in the hardware (such as better sample rate conversion done by a DSP),
theSound Manager will allow this support to be passed off to the hardware for better
quality and efficiency.
Support for plug-in audio codecs is another significant new feature. This allows the
Sound Manager to support new compression methods, which become desirable now that
we're supporting 16-bit data.
Sound Manager 3.0 was developed by Jim Reekes and Kip Olson. Kip wants everyone to
know that the original design document describing the Sound Manager back in 1987
was titled "Software Architecture for a Device-Independent Sound Manager," which
can be abbreviated as SADISM. This explains a lot, doesn't it?*
Sound Manager 3.0 has been made widely available. The extension, control panel, and
related files are not only on this issue's CD but are also included in the Sound Manager
Developer's Kit v. 3.0 available from APDA, in Hardware System Update 2.0, with
sound products from third parties, and on various electronic bulletin boards (such as
CompuServe and America Online). Sound Manager 3.0 is built into some new Macintosh
systems; you can tell it's there if Sound Out is listed in the Sound control panel. *
JIM REEKES studied music composition and theory in college, never taking a single
computer science or engineering class because he knew they would pollute his brain.
He taught himself programming, beginning with the Apple II and then on the Macintosh
128K in 1984. He began working in Apple's Developer Technical Support group in
1988. He took over responsibility for the Sound Manager during System 7 beta (so
you can't blame that one on him!) and recently finished Sound Manager 3.0, a complete
rewrite. If there's one thing he has learned while at Apple, it's that there's a fine line
between amazing insight and having a bad attitude. Jim has been collecting progressive
rock and electronic music recordings since the 1970s. He grew up in Pomona,
California, during the 1960s and can remember when Frank Zappa performed in local
bars on Mission Blvd. and Cucamonga was a vineyard. He wishes programming didn't
burn out his creative drive so that he could spend more time in his MIDI studio. *
Thanks to Ray Chiang and Bryan ("Beaker") Ressler for reviewing this column.
Special thanks to Kip Olson. *