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stft <- function(X, win=min(80,floor(length(X)/10)),
inc=min(24, floor(length(X)/30)), coef=64,
wtype="hanning.window")
{
numcoef <- 2*coef
if (win > numcoef)
{
win <- numcoef
cat ("stft: window size adjusted to", win, ".\n")
}
numwin <- trunc ((length(X) - win) / inc)
## compute the windows coefficients
wincoef <- eval(parse(text=wtype))(win)
## create a matrix Z whose columns contain the windowed time-slices
z <- matrix (0, numwin + 1, numcoef)
y <- z
st <- 1
for (i in 0:numwin)
{
z[i+1, 1:win] <- X[st:(st+win-1)] * wincoef
y[i+1,] <- fft(z[i+1,])
st <- st + inc
}
Y<- list (values = Mod(y[,1:coef]), windowsize=win, increment=inc,
windowtype=wtype)
class(Y) <- "stft"
return(Y)
}
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