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C-3
Editing Tools and Data Preparation
C.2 Data Preparation
The MSP53C691 slave synthesizer supports several speech synthesis
algorithms. The speech data sent to the slave device must match the format
defined by TI or generated by a TI’s tool (SDS6000 for MELP, CELP, or
ADPCM). The data preparation for the MSP53C691 using different algorithms
is discussed in the following paragraphs.
C.2.1 ADPCM
A WAV file can be encoded in ADPCM through the SDS6000 software tool.
The bit rate for ADPCM is: (sampling rate)*16 bits/4. For example, an 8-kHz
WAV file produces 32 kbps of encoded data.
C.2.2 MELP and CELP
The SDS6000 is used to convert an input audio data file into MELP or CELP
data formats. The input data file must be in .WAV format. The audio data must
be sampled at either 8 kHz, 10 kHz, or 11KHz and must have 16-bit-signed pre-
cision.
See the
Tips for Optimal TI Speech appendix for details about recording and
preprocessing a file.
Note:
While processing a music file in CELP, it is advisable to check the Music but-
ton before processing. The file is processed at a slightly higher bit rate in this
selection so enhancing the quality of the compressed file. Please see the
HELP in SDS6000 for details.
The sound files must start and stop at a level close to zero; errors may result
otherwise. The volume of the sound files must also be adjusted to a peak-to-
peak level around 0.5 V to –0.5 V (assume full scale is 1 V to –1 V). Clipping
may result if the sound file is too loud after the encoding. Additionally, if the
wave file is sampled at a higher rate (CD quality sound file 44.1-kHz sampling
or DAT in 48-kHz), resampling to 8 kHz or 10 kHz is necessary before the con-
version. Filtering and renormalizing may be necessary during downsampling
to reduce aliasing and noise.
There are several software programs available to perform this resampling
function. Two commonly available examples are GoldWave and Cool Edit Pro.
GoldWave is a shareware program that provides editing function on sound
files in a Windows environment. This software can be downloaded from the
following web site: http://www.goldwave.com.
To resample the original wave/sound file, the high-frequency portion must be
filtered first to eliminate the aliasing in resampling. All frequencies above one
half of the final sampling rate must be removed from the sound file. For exam-
ple, before converting the sampling rate to 8 kHz, the data must be filtered to
remove all frequency components above 4 kHz. Some sound editing tools
Summary of Contents for MSP53C691
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