NAME
atsa - Performs ATS analysis on a soundfile. .
DESCRIPTION
ATS analysis for use with the Csound ATS Resynthesis opcodes.
SYNTAX
csound -U atsa [flags] infilename outfilename
INITIALIZATION
The following flags can be set for atsa (The default values are stated
in parenthesis):
-b start (0.000000 seconds)
-e duration (0.000000 seconds or end)
-l lowest frequency (20.000000 Hertz)
-H highest frequency (20000.000000 Hertz)
-d frequency deviation (0.100000 of partial freq.)
-c window cycles (4 cycles)
-w window type (type: 1) (Options: 0=BLACKMAN, 1=BLACKMAN_H,
2=HAMMING, 3=VONHANN)
-h hop size (0.250000 of window size)
-m lowest magnitude (-60.000000)
-t track length (3 frames)
-s min. segment length (3 frames)
-g min. gap length (3 frames)
-T SMR threshold (30.000000 dB SPL)
-S min. segment SMR (60.000000 dB SPL)
-P last peak contribution (0.000000 of last peak´s parameters)
-M SMR contribution (0.500000)
-F File Type (type: 4) (Options: 1=amp.and freq. only,
2=amp.,freq. and phase, 3=amp.,freq. and residual,
4=amp.,freq.,phase, and residual)
PARAMETERS
ATS analysis was devised by Juan Pampin. For complete information on
ATS visit: http://www-ccrma.stanford.edu/~juan/ATS.html.
Analysis parameters must be carefully tuned for the Analysis Algorithm
(ATSA) to properly capture the nature of the signal to be analyzed. As
there are a significant number of them, ATSH offers the possibility of
Saving/Loading them in a Binary File carrying the extension "*.apf".
The extension is not mandatory, but recommended. A brief explanation of
each Analysis Parameters follows:
1. Start (secs.): the starting time of the analysis in seconds.
2. Duration (secs.): the duration time of the analysis in seconds. A
zero means the whole duration of the input sound file.
3. Lowest Frequency (Hz.): this parameter will partially determine the
size of the Analysis Window to be used. To compute the size of the
Analysis Window, the period of the Lowest Frequency in samples (SR
/ LF) is multiplied by the number of cycles of it the user wants to
fit in the Analysis Window (see parameter 6). This value is rounded
to the next power of two to determine the size of the FFT for the
analysis. The remaining samples are zero-padded. If the signal is a
single, harmonic sound, then the value of the Lowest Frequency
should be its fundamental frequency or a sub-harmonic of it. If it
is not harmonic, then its lowest significant frequency component
may be a good starting value.
4. Highest Frequency (Hz.): highest frequency to be taken into account
for Peak Detection. Once it is determined that no relevant
information is found beyond a certain frequency, the analysis may
be faster and more accurate setting the Highest Frequency parameter
to that value.
5. Frequency Deviation (Ratio): frequency deviation allowed for each
peak in the Peak Continuation Algorithm, as a ratio of the
frequency involved. For instance, considering a peak at 440 Hz and
a Deviation of .1 will produce that the Peak Continuation Algorithm
will only try to find candidates for its continuation between 396
and 484 Hz (10% above and below the frequency of the peak). A small
value is likely to produce more trajectories whilst a large value
will reduce them, but at the cost of rendering information
difficult to be further processed.
6. Number of Cycles of Lowest Frequency to fit in Analysis Window:
this will also partially determine the size of the Fourier Analysis
Window to be used. See Parameter 3. For single harmonic signals, it
is supposed to be more than one (typically 4).
7. Hop Size (Ratio): size of the gap between one Analysis Window and
the next expressed as a ratio of the Window Size. For instance, a
Hop Size value of .25 will "jump" by 512 samples (Windows will
overlap for a 75% of their size). This parameter will also
determine the size of the analysis frames obtained. Signals that
change their spectra very fast (such as Speech sounds) may need a
high frame rate in order to properly track their changes.
8. Amplitude Threshold (dB): the highest amplitude value to be taken
into account for Peak Detection.
9. Window Type: the shape of the smoothing function to be used for the
Fourier Analysis. There are four choices available at present:
Blackman, Blackman-Harris, Von Hann, and Hanning. Precise
specifications about them are easily found on D.S.P. bibliography.
10. Track Length (Frames): The Peak Continuation Algorithm will
"look-back" by Length frames in order to do its job better,
preventing frequency trajectories from curving too much and loosing
stability. However, a large value for this parameter will slow down
the analysis significantly.
11. Minimal Segment Length (Frames): once the analysis is done, the
spectral data can be further "cleaned" up during post-processing.
Trajectories shorter than this value are suppressed if their
average SMR is below Minimal Segment SMR (see parameters 16 and
14). This might help to avoid non-relevant sudden changes while
keeping a high frame rate, reducing also the number of intermittent
sinusoids during synthesis.
12. Minimal Gap Length (Frames): as parameter 11, this one is also used
to clean up the data during post-processing. In this case, gaps
(zero amplitude values, i.e. theoretical "silence") longer than
Length frames are filled up with amplitude/frequency values
obtained by linear interpolation of the adjacent active frames.
This parameter prevents sudden interruptions of stable trajectories
while keeping a high frame rate.
13. SMR Threshold (dB SPL): also a post-processing parameter, the SMR
Threshold is used to eliminate partials with low averages.
14. Minimal Segment SMR (dB SPL): this parameter is used in combination
with parameter 11. Short segments with SMR average below this value
will be removed during post-processing.
15. Last Peak Contribution (0 to 1): as explained in Parameter 10, the
Peak Continuation Algorithm "looks-back" several number of frames
to do its job better. This parameter will help to weight the
contribution of the first precedent peak over the others. A zero
value means that all precedent peaks (to the size of Parameter 10)
are equally taken in account.
16. SMR Contribution (0 to 1): In addition to the proximity in
frequency of the peaks, the ATS Peak Continuation Algorithm may use
psycho-acoustic information (the Signal-to-Mask-Ratio, or SMR) to
improve the perceptual results. This parameter indicates how much
the SMR information is used during tracking. For instance, a value
of .5 makes the Peak Continuation Algorithm to use a 50% of SMR
information and a 50% of Frequency Proximity information to decide
which is the best candidate to continue a sinusoidal track.
EXAMPLES
The following command:
atsa -b0.1 -e1 -l100 -H10000 -w2 audiofile.wav audiofile.ats
Generates the ATS analysis file ´audiofile.ats´ from the original
´audiofile.wav´ file. It begins analysis from second 0.1 of the file
and the analysis is performed for 1 second thereafter. The lowest
frequency stored is 100 Hz and the highest is 10kHz. A Hamming window
is used for each analysis frame.
AUTHORS
Barry Vercoe
MIT Media Lab
Author.
Dan Ellis
MIT Media Lab,
Cambridge
Massachussetts
Author.
COPYRIGHT