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Archive-name: sgi/faq/audio
Last-modified: Sun Sep 18 13:01:54 CDT 1994

    SGI audio Frequently Asked Questions (FAQ)

This is one of the Silicon Graphics FAQ series, which consists of:

    SGI admin FAQ - IRIX system administration
    SGI apps FAQ - Applications and miscellaneous programming
    SGI audio FAQ - Audio applications and programming
    SGI graphics FAQ - Graphics and user environment customization
    SGI hardware FAQ - Hardware
    SGI Impressario FAQ - IRIS Impressario
    SGI Inventor FAQ - IRIS Inventor
    SGI misc FAQ - Introduction & miscellaneous information
    SGI movie FAQ - Movies
    SGI Performer FAQ - IRIS Performer
    SGI pointer FAQ - Pointer to the other FAQs

Read the misc FAQ for information about the FAQs themselves.  Each FAQ
is posted to comp.sys.sgi.misc and to the news.answers and comp.answers
newsgroups (whose purpose is to store FAQs) twice per month.  If you
can't find one of the FAQs with your news program, you can get it by
anonymous FTP from one of these sites:

    rtfm.mit.edu:/pub/usenet/comp.sys.sgi.misc/
    rtfm.mit.edu:/pub/usenet/news.answers/sgi/faq/
    rtfm.mit.edu:/pub/usenet/comp.answers/sgi/faq/
    viz.tamu.edu:/pub/sgi/faq/

Note that rtfm.mit.edu is home to many other FAQs and informational
documents, and is a good place to look if you can't find an answer
here. If you can't use FTP, send mail to mail-server@rtfm.mit.edu with
the command 'send usenet/news.answers/ftp-list/faq' on a line by itself
in the text, and it will send you a document describing how to FTP by
mail. You can also read a hypertext version of the FAQs at

    http://www.cis.ohio-state.edu/hypertext/faq/usenet/sgi/top.html

The SGI FAQs are freely distributable and we encourage wide circulation.
The contents are accurate as far as we know, but the usual disclaimers
apply. Please send additions and changes to sgi-faq@viz.tamu.edu.

Topics covered in this FAQ:
---------------------------
   -1- How do I program the Motorola 56000 DSP on the Indigo (R3K and
       R4K)?
   -2- How do I connect my stereo to my Ind{igo,igo2,y}?
   -3- How do I change the volume of the audio out the back of my
       machine?
   -4- Indigo2 speaker seems quieter than my Indigo. Am I imagining
       things?
   -5- I need to crank up the input gain on Indigo2 to use the
       microphone successfully. What's the scoop?
   -6- The glossy paper says that Indigo2 and Indy have 4-channel input
       and output. That sounds really cool. How do I use it?
   -7- Okay, so 4-channels of input and output is great, but I need
       more. Can I get more channels of audio for my machine?
   -8- Now that I have IRIX 5.X, I can't seem to find audio.h and
       libaudio.a in order to compile my audio code. What gives?
   -9- I like the boot tune, but it's just a bit too loud. How do I tone
       it down a bit?
  -10- How can I change the output speaker/headphone volume from a shell
       script?
  -11- What 3rd party audio solutions exist for Silicon Graphics
       machines?
  -12- I'd like to write my own audio programs. How do I get started?

----------------------------------------------------------------------

Subject:    -1- How do I program the Motorola 56000 DSP on the Indigo
                (R3K and R4K)?
Date: 20 Aug 94 00:00:01 EST

Short answer: You don't.

Long answer: The DSP on the Indigo is used exclusively by the audio
system: whenever you are using the audio, you are using the DSP.

In order to insure that audio processes are serviced, access to the DSP
is limited to the audio device driver which performs all functions on
behalf of application programs.

Moreover, any code developed for the DSP on the Indigo may not work on
other systems since the DSP is not guaranteed to be present. For
instance, Indigo2 and Indy do not have a DSP. Audio is supported by a
combination of code running on the CPU and a audio ASIC chip. SGI
supports the Audio Library software inter- face as opposed to any
particular hardware implementation of the audio system.

Lastly, any signal processing code developed on the host CPU benefits
from speed increases of the CPU (and this code is easier to write as
well).

------------------------------

Subject:    -2- How do I connect my stereo to my Ind{igo,igo2,y}?
Date: 20 Aug 94 00:00:01 EST

The Line in and Line out levels have been designed to be directly
connected to conventional stereo systems.

One way to do it is to connect it up as if the computer was a tape
recorder.  Line out on the computer connects to Rec in on the stereo
and Line in connects to Rec out.

------------------------------

Subject:    -3- How do I change the volume of the audio out the back of
                my machine?
Date: 20 Aug 94 00:00:01 EST

The headphone and speaker volume is adjusted using apanel(1). The
sliders under the 'Speaker' label control the output volume of the
speaker and headphone. The line-level output voltage is not affected.

------------------------------

Subject:    -4- Indigo2 speaker seems quieter than my Indigo. Am I
                imagining things?
Date: 20 Aug 94 00:00:01 EST

No, this is not a figment of the imagination. There are two factors at
work that make the Indigo2 quieter than Indigo: 1) the speaker amp is
less powerful on Indigo2; 2) the system fan on Indigo2 is louder than
the Indigo fan. These two things lead to a quiet speaker that seems
even quieter. See the release notes for more information.

------------------------------

Subject:    -5- I need to crank up the input gain on Indigo2 to use the
                microphone successfully. What's the scoop?
Date: 20 Aug 94 00:00:01 EST

The Indigo2 and Indy both have less input gain than the Indigo and
4D/35. However, all have plenty of gain to operate the microphone.  On
the Indigo2 and Indy, you have to set the input gain to a larger
nominal level.

------------------------------

Subject:    -6- The glossy paper says that Indigo2 and Indy have 4-
                channel input and output. That sounds really cool. How
                do I use it?
Date: 20 Aug 94 00:00:01 EST

In order to enable 4-channel audio, you must choose "4-channel mode"
from the 'Options' menu of apanel or make a call in your program to
ALsetparams(3A). See the man page for ALsetparams(3A) for more infor-
mation.

Enabling the 4-channel mode will cause the electrical char- acteristics
of your audio connections to change: the headphone jack will become a
second line-level output (like the normal line-level output). The mic
input will become a second line-level input *if* you have 'line'
selected as your input source. If you have the input source set to
'mic', then the mic input will continue to behave as a microphone
input.

Lastly, when your machine is in 4-channel mode, the input and output
sample rates will be locked together. Thus, changing the input or
output rate in this mode will affect the output or input rate,
respectively.

You may also run 4-channel applications when the audio system in in
2-channel mode, and vice versa (2-channel applications work when the
system is in 4-channel mode).

------------------------------

Subject:    -7- Okay, so 4-channels of input and output is great, but I
                need more. Can I get more channels of audio for my
                machine?
Date: 20 Aug 94 00:00:01 EST

Sonic Solutions (San Raphael, CA) has announced that it is porting
Sonic System to SGI platforms. See below.

------------------------------

Subject:    -8- Now that I have IRIX 5.X, I can't seem to find audio.h
                and libaudio.a in order to compile my audio code. What
                gives?
Date: 20 Aug 94 00:00:01 EST

The #include file audio.h and the library libaudio.a became a part of
the "Digital Media Developement Option" (dmdev) in IRIX 5.X.  Dmdev
contains more than just the audio development libraries, and it is
available for an extra fee. If you are like many people and think this
is a bogus situation, tell your salesperson.

------------------------------

Subject:    -9- I like the boot tune, but it's just a bit too loud. How
                do I tone it down a bit?
Date: 20 Aug 94 00:00:01 EST

The boot tune volume is controlled by the 'volume' variable used by the
system PROM. The value for 'volume' can be set in the range [0-255],
where lower numbers represent a lower boot tune volume.  A 'volume'
value of 0 disables the boot tune, viz. the tune is not played at all.
The value of 'volume' can be set in the PROM monitor or using the
nvram(1M) command.

------------------------------

Subject:   -10- How can I change the output speaker/headphone volume
                from a shell script?
Date: 20 Aug 94 00:00:01 EST

You can use two methods to do this: 1) apanel -nodisplay or volume.c
program (this program can be found in ~4Dgifts/examples/ libaudio
directory).

------------------------------

Subject:   -11- What 3rd party audio solutions exist for Silicon
                Graphics machines?
Date: 20 Aug 94 00:00:01 EST

Doug Cook <cook@sgi.com> maintains a list of "Audio Applications for
Silicon Graphics Systems" which he posts to comp.sys.sgi.audio. A copy
is at viz.tamu.edu:/pub/sgi/lists/audio-apps.

------------------------------

Subject:   -12- I'd like to write my own audio programs. How do I get
                started?
Date: 20 Aug 94 00:00:01 EST

First, for 5.2 systems you need the Digital Media Development Option.
From Michael Portuesi (portuesi@sgi.com):

The Digital Media Development Option contains the Video, Audio, Audio
File, MIDI, CD, DAT, Movie, and Compression Libraries for your digital
media programming enjoyment.

The part number for the Digital Media Development Option is
SC4-DMDEV-2.0.   If you would like to develop applications which
manipulate QuickTime files, you must also order the companion product,
QuickTime 1.0 Compressor Library, part number SC4-QTCL-1.0.

In the United States, you can order these products by calling Silicon
Graphics toll-free at 1-800-800-SGI1 (1-800-800-7441).  If you live in
a country other than the United States, contact your nearest Silicon
Graphics office, or call one of these regional telephone numbers:

Europe                  (41) 22-798.75.25       (Geneva, CH)
North Pacific           (81) 3-5420.71.10
South Pacific           (61) 2-879.95.00
Latin America           1(415) 390.46.37
Canada                  1(416) 625-4747

For audio, example code is contained in ~4Dgifts/examples/libaudio.
This example code comes with the DMDEV option.  Other code
demonstrating the use of the CD and DAT audio libraries can be found in
a 'tar' file at ftp.sgi.com:~ftp/sgi/dat.

------------------------------

End of sgi/faq/audio Digest
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