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Speech recognition Algorithm:

This  input the speech signal  is in time domain we
convert it into frequency domain because in time domain sound can be easily
differentiate from one another.

Actually when we convert it into the frequency
domain the speech attributes become visible in the frequency domain which is not
visible in the time domain.

Fast Fourier transform is nothing but it is an
algorithm for implementing Fourier transform. Basically, it is a method of
implementing the algorithm .these are for implementaion.we use fast Fourier
transform because it is an efficient algorithm

If we take Fourier transform of this sound.signal
Fourier transform will give us frequencies overall in this sound signal. This
Fourier transform gives us overall frequencies contained in this speech signal.In
speech recognition not all of these frequencies are helpful because it is not
our aim to find out how much frequencies are contained in this speech
signal

fff   fff   
ffff

Secondly, we need time information with these
frequencies. Fourier transform provides us combined frequencies of all the
sound with no time information. what frequency at what time.

STFT:

Short time means that instead of taking the
Fourier transform of the whole sound signal.we just pick a signal of 10msec
duration from the above sound signal.

S            H             E

|

10ms

S             H

10ms

Then 10ms for H and take Fourier to transform so we
get frequencies in     H    E   
region

The advantages are that we get some time
information. But the disadvantages is that when we take this sharp 10ms then signal
edges which are called leakage or cut signal.

so it gives us additional frequencies which are
called wrong frequencies.sharp edges are due to wrong frequencies.

To eliminate these wrong frequencies or sharp
edges or discontinuities at the input signal and at the end Windowing is
performed

In windowing 
rather than 10ms. we will take 25ms duration and take the Fourier transform
of these signals.And then associate these frequencies in the middle. that is found from the Fourier transform.

Window duration is usually taken double than the
frame duration. The basic purpose of windowing is to smooth the sharp edges in the 25ms. Due to the high duration, these sharp edges become smooth.

There is also a limit for window length.if we
increase much more then double then the other characteristics will also count
in it. Usually, take double the windowing then the frame duration.

Windowing duration  =  2 Frame duration

Human ear working:

Let suppose initially frequencies from  0 to 500 Hz 
.the change in sound means change in its loudness is L.

At high frequencies, the change in loudness is not
proportion.so what we do to it change it to linear. We convert the Hz scale into
mel scale. So what is mel scale conversion? In it, we just map that frequencies
of 500Hz to f1 frequency 700Hz to f2 frequency and 1000Hz to f3 frequency.

Log(spectrum)  when we take the log of
the spectrum then it is             known
as a log spectrum.

When we take a log and after log, we take DCT of
spectrum then it is known as cepstrum. Here it contains frequency components but
these components are in mel frequency coefficients.

HMM:

we picked 13 features from MFCC. It is assumed
that these 13 features are the most discriminative features..take the example
of our eyes. hand etc. It is our feature but they are not discriminative mean they
are not helpful. As we have more feature but we are taking only 13 features
which are considered to be the most discriminative feature.

for a the thirteen feature model is designed.From
model we mean that for a the thirteen features has the following values
like  1,2,3,4,6---------13 as example

when a new test data has arrived in HMM.Hmm
extract 13 features from that test data and compared it with these models. After
comparison it gets finds whether it is A, B, C, or D vice versa.

Speech recognition Algorithm:

Speech recognition Algorithm: X(t) = Input speech signal. This input the speech signal is in time domain we convert it into freque...

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Speech recognition Algorithm:

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