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3. _A_u_d_i_o__I_/_O__S_y_s_t_e_m
An audio I/O system is included with most Silicon Graphics
workstations, including Indy, Indigo, Onyx2, OCTANE, and
O2. Audio is an optional feature available for Origin,
Onyx, Challenge and Power Challenge machines. This section
details the changes, known bugs, and caveats in the audio
system itself. See other sections of these release notes for
information on sound utility commands and graphical user
interface tools for recording, editing, and playback, as
well as CD audio, DAT audio, sound synthesis, and other
features.
The audio execution environment _d_m_e_d_i_a__e_o_e._s_w._a_u_d_i_o includes
basic kernel software to support SGI audio I/O devices as
well as o32, n32, and 64-bit versions of the Audio Library
DSO, libaudio.so. The Digital Media Tools image
(_d_m_e_d_i_a__e_o_e._s_w._t_o_o_l_s) contains most of the audio tools, such
as _a_p_a_n_e_l(_1) and _s_o_u_n_d_p_l_a_y_e_r(_1).
3.1 _C_h_a_n_g_e_s__a_n_d__A_d_d_i_t_i_o_n_s
This section describes changes/additions to the audio I/O
system between the IRIX 6.2 and IRIX 6.5 releases. The
audio system provided with all OCTANE and Onyx2 systems
supports a new eight-channel digital audio ADAT interface.
This is in addition to the analog and two-channel digital
audio interfaces as provided in previous workstations. The
audio system also supports a Professional Digital Audio
Option, which has additional ADAT and AES I/O.
The audio system in IRIX 6.3, IRIX 6.4, and IRIX 6.5 is
based on a new Audio Library (2.0) which supports multiple
audio I/O devices in a single system.
+o The audio system now supports multiple audio devices.
On systems which have more than one independent input
and output, you can now select the audio devices you
wish your applications to use. Applications can use
multiple devices simultaneously.
+o The audio system now supports a wider variety of audio
devices. Some of the new devices include the 8-channel
ADAT I/O and the 16-channel SMPTE 272M digital I/O on
the DIVO video option for Onyx2.
+o The audio system supports sample rates that are slaved
to video sources. Only some devices support this; look
- 2 -
under "Preferences" for the device in the Audio Control
Panel.
+o The microphone and line-input gains are now
independent. This means you seldom need to adjust the
input gain when you change input sources. Now when you
select a new input source, the gain will automatically
revert to its value when that source was previously
selected.
+o The audio system now provides support for reading and
writing digital audio subcode. You can select
consumer-mode or professional-mode subcode on the AES
digital output using the Audio Control Panel. This
allows the AES output to work with a wider variety of
devices, since some devices require a particular kind
of subcode.
+o The Audio Control Panel has been generalized to support
multiple audio I/O devices. See the "Audio Control
Panel" chapter of these release notes for more
information.
+o The Audio Library is now a DSO rather than a statically
linked library. Applications which were linked with
libaudio.a (in releases prior to IRIX 6.3) will
continue to function properly on IRIX 6.5.
+o Indigo R4000 (IP20) has full support for AL 2.0,
including features previously available on that machine
under AL 1.0, such as precise synchronization support.
Correctly written AL 2.0 applications will now work
across all supported IRIX 6.5 configurations.
3.2 _B_u_g__F_i_x_e_s
This section lists the audio system bugs fixed in IRIX 6.5.
+o A problem existed in IRIX 6.2 where a rare race-
condition could panic the system if a multi-process
application closed an audio port in one process while
it attempted to use the port in another process. (SCR
334606)
+o Prior to IRIX 6.5, there was no way to choose between
consumer-mode and professional-mode subcode on AES
output. This caused the AES output to fail with some
devices requiring a particular subcode format. (SCR
578672).
- 3 -
+o On O2 only, there was a chip bug which, under extremely
rare circumstances, could cause data corruption. This
has been worked around (SCR 568567 and 568568).
3.3 _C_a_v_e_a_t_s
+o On Onyx2, OCTANE, or with the PCI digital audio option,
some digital audio devices
which use S/PDIF ("consumer") signals (.5V peak-to-
peak) may not work reliably with the AES digital input.
This input primarily supports AES-3id signals (1V
peak-to-peak).
+o On Onyx2, OCTANE, or with the PCI digital audio option,
the audio software currently supports both AES3
("professional") subcode format and S/PDIF ("consumer")
subcode on the AES digital output. Some devices may
only work with one or the other format. If you have
difficulty getting the output to work with some device,
try switching the subcode format. You can do this using
_a_p_a_n_e_l by selecting "preferences" for the AES Out
device. Note that the AES digital input accepts either
subcode format.
+o The Onyx2, OCTANE, and O2 systems do not support four-
channel analog mode. They do however support eight-
channel digital audio I/O (O2 requires the PCI
Professional Audio Option) and have compatibility so
that programs that ask for four-channel ports will use
the first four channels of the eight-channel ADAT port.
+o On Onyx2, OCTANE, and O2 systems, the audio panel
application (apanel) can display the rate of the AES
digital input. However, the display will be invalid
after rebooting the system until audio is started for
the first time. Likewise, applications which query the
digital input sample rate will receive invalid results
until audio is first started. The workaround is to
start (and optionally then stop) audio before using the
digital input rate. This can be accomplished, for
example, by briefly enabling a "Meter" in apanel.
+o On Onyx2, when using video locking, only "NTSC"
(525/59.94) and "PAL" (625/50) timings are supported.
The audio software switches between them automatically.
If an invalid video signal is present, lock will be
lost and the device will revert to its nominal rate.
+o On Onyx2, video lock will not work after rebooting the
system until audio is started for the first time. This
- 4 -
particularly affects AES and ADAT digital outputs:
while these output can be used as clock inputs to other
devices even when audio is not running, these output's
sample rates will not be locked to video until audio is
started for the first time.
+o In some systems including Indy, Indigo and
Audio/Serial Option, the digital input could be used to
monitor or record the output of audio applications when
nothing was plugged into the digital I/O jack. You will
need an external loopback cable to accomplish this on
Onyx2, OCTANE, and O2, because the jacks are physically
separated.
+o The O2 system does not have a built-in digital I/O
jack. In some systems, the digital input could be used
to monitor or record the output of audio applications
when nothing was plugged into the digital I/O jack.
This feature does not work on O2 without the PCI
Professional Audio Option, which includes digital I/O.
+o The O2 audio system contains two independent digital-
to-analog converters (DACs). Device "AnalogOut"
represents the DAC that drives the internal speaker,
headphone output, and the line-out connectors on the
side panel of the system. The volume buttons will
affect the gain on this device, including line-out.
Device "AnalogOut2" represents the DAC that drives the
line-out connectors on the rear panel of the system.
The volume buttons do not affect gain on "AnalogOut2".
Audio signals played through one device will not be
heard on the other. For example, audio sent to device
"AnalogOut2" will not be heard on the internal speaker,
the headphones, or the line-out connectors on the
system side panel. A method for connecting multiple
devices together at the system level is planned for a
subsequent release.