cl_aware, CLaware - Aware Audio Schemes in the Compression Library
This man page describes the Aware audio compression algorithms that are
installed in the Compression Library (CL). Two Aware schemes are
1. CL_MPEG1_AUDIO_AWARE The ISO/MPEG-audio standard algorithm
with layers I and II.
2. CL_MULTIRATE_AWARE The Aware-proprietary MultiRate I
lossless or low-distortion algorithm.
Each scheme is accessed through the standard CL API, described in
CLintro(3dm). Listed below are the parameters that may be used with
these two codecs. Note that parameters described in cl_mpeg1(3dm) are
currently not supported for CL_MPEG1_AUDIO_AWARE.
PARAMETERS : GENERAL CL
The following general CL parameters are useful for the Aware codecs.
CL_FORMAT [Toc] [Back]
Indicates the format of the components of the original uncompressed
audio. Default is CL_FORMAT_STEREO_INTERLEAVED, legal alternative
CL_BITS_PER_COMPONENT [Toc] [Back]
Informs the scheme of the width of the audio samples (assumed to
be linear two's complement). Currently, the only supported value
CL_FRAME_RATE [Toc] [Back]
Tells the scheme the sampling rate of the uncompressed audio.
Default is 44100.0 Hz. Legal values for the MPEG algorithm are
32000.0, 44100.0, and 48000.0 Hz. Legal values for the MultiRate
algorithm are 8000.0, 11025.0, 16000.0, 22050.0, 32000.0, 44100.0,
and 48000.0 Hz.
CL_COMPRESSION_RATIO [Toc] [Back]
A read-only parameter.
CL_EXACT_COMPRESSION_RATIO [Toc] [Back]
A read-only parameter. It is true if CL_COMPRESSION_RATIO is
exact, and false if the ratio is a worst-case estimate.
CL_FRAMES_PER_CHUNK [Toc] [Back]
A read-only parameter. This is the number of audio frames which
are compressed at one time by the scheme. The data that are passed
to clCompress should be in multiples of this size.
CL_FRAME_TYPE [Toc] [Back]
A read-only parameter. Indicates the status of the next frame to be
processed is either CL_KEYFRAME (i.e. the first frame in a compressed
chunk) or CL_PREDICTED (all other alignments). This should always be
CL_KEYFRAME if the CL_FRAMES_PER_CHUNK parameter is followed. Note
that this definition is somewhat different than the general usage
given in CLintro(3dm).
CL_SPEED [Toc] [Back]
The CL_SPEED parameter takes values from 1.0 to 100.0. It has no
effect during compression. During decompression, it controls the
computational complexity by controlling several factors:
sample rate decimation, combining of stereo channels, filter shape
(MPEG only), and lossy_decode (MultiRate only).
The user of this parameter should be advised that changing it may
cause the sampling rate, total number of sample frames available,
and sample frames per compressed chunk to be changed.
After modifying this parameter, the values of CL_FRAME_RATE and
CL_FRAMES_PER_CHUNK should be queried for their new values.
PARAMETERS : AWARE
These parameters are specific to the Aware codecs.
CL_AWARE_CHANNEL_POLICY [Toc] [Back]
Selects the treatment of stereo signals.
CL_AWARE_STEREO indicates that the channels are part of a
single multi-channel signal.
CL_AWARE_JOINT_STEREO stereo redundancy exploited by coding high
frequency subbands together. Not supported
under MultiRate algorithm.
CL_AWARE_INDEPENDENT the channels are unrelated and coded
separately; e.g. multilingual sound tracks.
Note that any of these options are equivalent for single channel
CL_AWARE_BITRATE_POLICY [Toc] [Back]
Provides for different modes of bit assignment:
CL_AWARE_FIXED_RATE (MPEG only) A fixed bitrate is used to code
all of the channels. This is the default for
MPEG audio. See CL_AWARE_BITRATE_TARGET.
CL_AWARE_CONST_QUAL bitrate allowed to vary to satisfy MPEG
psychoacoustic model or MultiRate data
requirements (90+dB). This is the default
for the MultiRate algorithm. See
CL_AWARE_LOSSLESS (MultiRate only) The data is coded losslessly.
CL_AWARE_NOISE_MARGIN [Toc] [Back]
Used in conjunction with CL_AWARE_CONST_QUAL. Provides for
specification of the noise-to-mask ratio in MPEG psychoaccoustics:
Zero yields a theoretic psychoacoustic imperceptible compression.
Positive values provide more compression and noise becomes audible.
Negative values cause less compression and less perceptible noise.
For MultiRate, sets the noise-floor at -90 dB below the signal level.
This is the only valid MultiRate setting at this time.
CL_AWARE_BITRATE_TARGET [Toc] [Back]
(MPEG only) Used in conjunction with CL_AWARE_FIXED_RATE.
Determines the output data rate in bits per second. The allowed
MPEG layer I:
32000, 64000, 96000, 128000, 160000, 192000, 224000
256000, 228000, 320000, 352000, 384000, 416000, 448000
MPEG layer II:
32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000,
160000, 192000, 224000, 256000, 320000, 384000
CL_AWARE_LAYER [Toc] [Back]
(MPEG only) Selects the MPEG layer. Default is
CL_AWARE_MPEG_LAYER_II for layer II, other legal value is
CL_AWARE_MPEG_LAYER_I for layer I.
Aware compression is also accessible through the Audio File Library. For
more information see AFaware(3dm).
In order to use these schemes, a NetLS license needs to be obtained from
One Memorial Drive
Cambridge, MA 02142 USA
phone: (617) 577-1700
fax: (617) 577-1710
mpeg(4), CLintro(3dm), cl_mpeg1(3dm), aware(5), AFaware(3dm)
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