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1995-09-11
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3. _D_i_g_i_t_a_l__A_u_d_i_o
An IRIS Audio Processor is included with the Personal IRIS
4D/3X, IRIS Indigo, Indigo, and Indy systems. Included
with the audio system are a number of utility programs for
recording, processing, and playing digital audio. This
section details the changes, known bugs, and caveats in the
audio system itself, as well as in most of the bundled audio
utilities. The exceptions to this are _s_o_u_n_d_e_d_i_t_o_r,
_s_o_u_n_d_f_i_l_e_r, _c_d_m_a_n, and _d_a_t_m_a_n, for which release notes may
be found under the "Digital Media Tools" section.
3.1 _A_u_d_i_o__S_y_s_t_e_m
3.1.1 _C_h_a_n_g_e_s__a_n_d__A_d_d_i_t_i_o_n_s The audio system in IRIS
Digital Media Execution Environment 5.5 is the same as the
5.3 version.
This section lists changes and additions made between the
5.2 and 5.3 releases.
+o IRIX 5.3 includes support for accurate synchronization
between audio and other media. For information on how
to use these new features, please refer to the
dmedia_dev release notes and the Digital Media
Programmer's Guide.
+o The performance of the monitor function has been
significantly improved. It requires substantially less
CPU and has much lower latency from input to output.
+o The audio driver is now dynamically loadable. It is
automatically registered on systems which have audio
capabilities, and will be loaded upon the first
attempted use of audio.
3.1.2 _B_u_g__F_i_x_e_s
+o 5.2 had some subtle problems with sample rates in
four-channel mode. These have been fixed in 5.3.
3.1.3 _C_a_v_e_a_t_s
- 2 -
+o When there is nothing physically connected to the
digital I/O jack, it is meaningless to set the system
sample rates in the following three ways:
+o output sample rate set to match the input sample
rate while using digital input as the system
input.
+o input sample rate set to the digital rate and the
output rate set to match the input rate.
+o input sample rate set to the digital rate and the
output rate set to the digital input rate.
When the system is put in any of these states, the
sample rate is undefined.
+o The IRIS Audio Processor hardware subsystem on all
platforms except 4D/35 and 4D/30 includes a direct
digital loopback channel, which makes a connection
between digital out and digital in when nothing is
plugged into the digital audio I/O jack. In effect,
this mechanism allows you to record the current output
of the machine by using the digital input when nothing
is connected to the digital I/O jack.
However, If you select Digital In on _a_u_d_i_o_p_a_n_e_l while
the direct digital loopback channel is enabled, then
select Monitor, you may hear feedback due to the
physical loopback channel.
Workaround: Avoid monitoring when Digital In is
selected and nothing is plugged into the digital I/O
jack (there's nothing to monitor in this case anyway).
An alternative is to keep a jack plugged into the
digital I/O jack (this doesn't have to be a live
connection) to physically defeat the loopback
mechanism.
3.2 _A_u_d_i_o__C_o_n_t_r_o_l__P_a_n_e_l__(_a_u_d_i_o_p_a_n_e_l_)
3.2.1 _C_h_a_n_g_e_s__a_n_d__A_d_d_i_t_i_o_n_s The Audio Control Panel in
IRIS Digital Media Execution Environment 5.5 is the same as
the 5.3 version.
This section lists changes and additions made between the
5.2 and 5.3 releases.
- 3 -
+o The on-line help information has been rewritten and
expanded.
+o Can specify AES (negative) input/output sampling rates
on command line as arguments to -rate options.
+o Added support under Options menu for control of audio
features in Indy Presenter LCD option. This menu item
appears only in the presence of the Presenter graphics
option.
3.2.2 _B_u_g__F_i_x_e_s
+o No longer crashes when switching from 2 channel to 4
channel mode with the metering function enabled.
+o Corrected delayed response of meters at low input
sampling rates.
+o audiopanel ignores X resource geometry dimensions but
now responds to coordinates. audiopanel does not
resize.
+o audiopanel now shows all sampling rates rates, 8.82 kHz
etc., and all AES rates, including Digital/2,
Digital/3, etc.
3.2.3 _K_n_o_w_n__P_r_o_b_l_e_m_s__a_n_d__W_o_r_k_a_r_o_u_n_d_s
+o If your environment variable DISPLAY is not set,
audiopanel will not run, even with -nodisplay option.
+o The input level meters do not reliably display signal
peaks. The primary cause is the presence of DC offset,
which is currently removed with a complementary box
filter of length 256. This algorithm removes only a
respectable amount of the DC offset at a minimum CPU
cost. The secondary cause is the audiopanel metering
routine does not keep up with the input sample stream
at rates above 32000 Hz.
+o The minimum input slider position does not correspond
to infinite attenuation on Indy and Indigo2. This is
an audio hardware limitation.
+o audiopanel configuration files may not contain empty
lines or comments after those that head the file.
- 4 -
3.3 _A_u_d_i_o__U_t_i_l_i_t_y__P_r_o_g_r_a_m_s
IRIS Digital Media Execution Environment 5.5 includes a
number of command-line utility programs that allow you to
record, play back, and process sound files:
The audio execution environment _d_m_e_d_i_a__e_o_e._s_w._a_u_d_i_o contains
the following command line utility programs:
+o _p_l_a_y_a_i_f_c(1) AIFF, AIFF-C sound file player
+o _p_l_a_y_a_i_f_f(1) installed as a symbolic link to
_p_l_a_y_a_i_f_c
+o _s_f_p_l_a_y(1) sound file player
+o _r_e_c_o_r_d_a_i_f_c(1) AIFF, AIFF-C sound file recorder
+o _r_e_c_o_r_d_a_i_f_f(1) installed as a symbolic link _r_e_c_o_r_d_a_i_f_c
+o _a_i_f_c_i_n_f_o(1) displays information about AIFF-C, AIFF
files
+o _s_f_i_n_f_o(1) displays information about sound files
+o _a_i_f_c_r_e_s_a_m_p_l_e(1) sampling rate conversion
utility
+o _a_i_f_f_2_a_i_f_c(1) converts an AIFF file to an
AIFF-C file
+o _a_i_f_c_2_a_i_f_f(1) converts an AIFF-C file to an AIFF file
+o _a_i_f_c_c_o_m_p_r_e_s_s(1) converts an AIFF or AIFF-C file to a
compressed format
+o _a_i_f_c_d_e_c_o_m_p_r_e_s_s(1) decompresses an AIFF-C file
+o _s_f_c_o_n_v_e_r_t(1) sound file conversion utility
+o _p_o_r_t_s_t_a_t(1) displays status of all open audio ports
on system
+o _r_b_v_i_e_w(1) graphically displays status of audio
ports
- 5 -
+o _p_a_s_s_t_h_r_u(1) user-level audio input monitor utility
The audio execution environment _d_m_e_d_i_a__e_o_e._s_w._a_u_d_i_o also
contains these DSO's (dynamically shared objects):
+o _l_i_b_a_u_d_i_o_f_i_l_e._s_o Audio File Library DSO
+o _l_i_b_a_u_d_i_o_u_t_i_l._s_o Audio Utility Library DSO
These DSO's have no dependencies on the IRIS Audio Library
or IRIS Audio Processor hardware. The Audio File Library
contains routines for performing AIFF/AIFF-C disk file
access. The Audio Utility Library contains low-level
routines for audio data conversion (most of these routines
are invoked internally from the Audio File Library).
Header files and programming guide information for the Audio
File Library and Audio Utility Library are included with
IRIS Digital Media Development Environment 5.3.
Aware,Inc compression routines are invoked internally from
the Audio File Library and Audio Utility Library. In order
to enable the Aware,Inc software codecs on your system, you
must purchase a NetLS license from Aware,Inc. See "Chapter
7: Compression Library Execution Environment" in these
release notes for more information.
Note that there are two different "families" of sound file
utility commands which overlap somewhat in functionality.
The first family of programs consists of _p_l_a_y_a_i_f[_f_c],
_r_e_c_o_r_d_a_i_f[_f_c], _a_i_f_c_i_n_f_o, _a_i_f_f_2_a_i_f_c, _a_i_f_c_2_a_i_f_f, _a_i_f_c_c_o_m_p_r_e_s_s,
_a_i_f_c_d_e_c_o_m_p_r_e_s_s, and _a_i_f_c_r_e_s_a_m_p_l_e. The second family consists
of _s_f_p_l_a_y, _s_f_i_n_f_o, and _s_f_c_o_n_v_e_r_t.
The first set of programs are built on top of the Silicon
Graphics Audio File Library, and support the audio
compression algorithms for AIFF-C, which are built into the
library (CCITT G.711 and CCITT G.722, Aware,Inc MPEG and
MultiRate codecs). 4DGifts source code for each of the
utilities (except for _a_i_f_c_r_e_s_a_m_p_l_e, which contains
proprietary high-quality rate-conversion code) is included
in the IRIS Digital Media Development Environment 5.3.
The second set of programs share source code with _S_o_u_n_d
_F_i_l_e_r (included in the IRIS Digital Media Tools 5.5
subsystem _d_m_e_d_i_a__t_o_o_l_s._s_w._s_o_u_n_d_t_o_o_l_s). These program
support additional file formats (NeXT/Sunr, Microsoftr RIFF
WAVE). However, they are not as full-featured as the
programs in the first set when it comes to AIFF and AIFF-C
- 6 -
files. For example, the file conversion programs in the
first set (_a_i_f_c_2_a_i_f_f, _a_i_f_c_r_e_s_a_m_p_l_e, etc) preserve the
auxiliary nonaudio data (loop points, author string,
application-specific data) stored in the various optional
AIFF-C (AIFF) header fields. _s_f_c_o_n_v_e_r_t does not preserve
these header chunks across conversions.
We are working to simplify this somewhat confusing situation
by merging corresponding tools from the two families (e.g.,
combine _p_l_a_y_a_i_f_c and _s_f_p_l_a_y into a single program which
supports both existing command-line interfaces). We hope
that new versions of the audio utilities will be available
by the next major IRIX release following 5.3.
3.3.1 _A_I_F_F_-_C__a_n_d__A_I_F_F__F_i_l_e__F_o_r_m_a_t_s Beginning with the
IRIX 4.0.1 software release, Silicon Graphics introduced
AIFF-C (Audio Interchange File Format with Compression
extensions) as its standard audio interchange file format.
The AIFF-C format is an extended version of the AIFF format,
supported by Silicon Graphics and Apple digital media
applications. AIFF-C files can store either compressed
audio data or standard linear PCM data, and optionally
include header fields that store many kinds of additional
information such as text, sample parameters, sample frame
markers, and application-defined data. AIFF is not a proper
subset of the AIFF-C format. AIFF-C adds new header fields
for compression scheme identification which break
compatibility with the older AIFF format.
By the IRIX 4.0.5F release, many of the digital media tools
such as Sound Editor (included in
_d_m_e_d_i_a__t_o_o_l_s._s_w._s_o_u_n_d_t_o_o_l_s) had been revised so that they
could read both AIFF and AIFF-C input files, but would write
only AIFF-C output files for both uncompressed and
compressed output. Unfortunately, many popular applications
for other platforms continue to support only the older AIFF
format. For the 5.3 release, many of the sound file
conversion utilities were modified so that the output file
retains the format of the input file.
3.3.2 _C_h_a_n_g_e_s__a_n_d__A_d_d_i_t_i_o_n_s This section lists changes
and additions since the 5.2 release.
+o The new program _p_o_r_t_s_t_a_t(1) prints the status of all
the currently open audio ports on a system.
+o The new program _r_b_v_i_e_w(1) graphically displays the
audio sample queue levels for all the open audio ports
- 7 -
on a system.
3.3.3 _B_u_g__F_i_x_e_s This section lists the bugs fixed since
the 5.2 release.
+o Restored sampling rate conversion algorithms for
_a_i_f_c_r_e_s_a_m_p_l_e and _s_f_c_o_n_v_e_r_t: due to a tragic
programming error, the IRIX 5.2 were rendered useless.
+o _a_i_f_c_r_e_s_a_m_p_l_e now outputs a compressed file when the
input file is compressed
This section lists the bugs fixed since version 5.4 of the
Digital Media Execution Environment.
+o Fixed sample rate conversion for the 48 kHz to 44.1 kHz
case for both _a_i_f_c_r_e_s_a_m_p_l_e and _s_f_c_o_n_v_e_r_t.
3.3.4 _K_n_o_w_n__P_r_o_b_l_e_m_s__a_n_d__W_o_r_k_a_r_o_u_n_d_s This section lists
known problems in the Digital Media Execution Environment
5.5 release, and ways to work around them.
+o MPEG audio, Awarer MultiRate and G.722 compression and
decompression schemes are CPU-intensive.
Workaround: To record or play back an AIFF-C file that
contains mono or stereo audio data compressed using
these algorithms, you might have to run _r_e_c_o_r_d_a_i_f_c(1)
or _p_l_a_y_a_i_f_c(1) with a nondegrading high priority. See
the man page _n_p_r_i(1) for information about how to do
this. An alternative is to record and play uncompressed
audio sample data, and compression/decompress the data
"offline" using the utilities _a_i_f_c_c_o_m_p_r_e_s_s(1) and
_a_i_f_c_d_e_c_o_m_p_r_e_s_s(1). These utilities are included in the
_d_m_e_d_i_a__t_o_o_l_s._s_w._s_o_u_n_d_t_o_o_l_s subsystem of IRIS Digital
Media Tools 5.3.
+o _p_l_a_y_a_i_f_c cannot decode the Apple proprietary
compression schemes (ACE/MAC algorithms) described in
the AIFF-C specification. Similarly, Mac sound
applications may not be able to decode AIFF-C data
which was encoded on an SGI workstation using MPEG
audio compression, Aware,Inc MultiRate compression,
G.722 compression, or G.711 compression.
- 8 -
Workaround: Always decompress AIFF-C audio data before
transferring between Macintosh and SGI systems.
+o _s_f_c_o_n_v_e_r_t now writes little-endian integer sample
files, but it does not yet write little-endian
floating-point output files. Currently, the only file
format that requires little-endian support is WAVE, and
it does not support floating point samples, so this is
an issue only when transferring raw floating point data
files between an SGI platform and a little-endian
machine.
+o _s_f_i_n_f_o omits some of the audio header information
stored in AIFF/AIFF-C files.
Workaround: use _a_i_f_c_i_n_f_o to obtain a more detailed
description of the audio data and auxiliary information
stored in an AIFF-C or AIFF file. Note that _a_i_f_c_i_n_f_o
understands only AIFF-C and AIFF files, while _s_f_i_n_f_o
understands several additional formats.
+o None of the AIFF-C conversion programs recognize the
comment-marker chunk described in the AIFF-C
specification. This chunk disappears when a file is
converted using one of the utilities.
+o The AIFF-C utility programs are not able to decode the
Apple proprietary audio compression schemes (ACE/MAC
algorithms) described in the AIFF-C specification.
Workaround: Always uncompress AIFF-C files before
transferring them from a Macintosh to an SGI platform.
+o _a_i_f_c_r_e_s_a_m_p_l_e does not modify the optional AES channel
status information in the AIFF-C file header to reflect
the new sampling rate.
Workaround: If the AES channel status information says
the audio data should be played at one rate, and the
AIFF-C (AIFF) file header says the audio data should be
played at another rate, go with sampling rate in the
file header.