<< Chapter < Page
  Speech synthesis   Page 1 / 1
Chapter >> Page >
This is an introductions to the specific techniques involved in the creation of a Pitch Corrector.

Time-domain vs. frequency-domain

Clearly, the goal of this algorithm is to take an input voice signal, change the pitch of the voice, and output the otherwise unaltered signal. In order to do so, the first step is to decide whether to analyze and manipulate these signals in the time domain or the frequency domain. Because our algorithm is primarily concerned with quickly identifying and shifting individual frequencies, we worked solely in the realm of the frequency domain. Of course, there are effective ways to deal with this problem without the frequency domain. However, as will later become obvious, there are some very useful techniques we developed that are not possible in the time domain. With pitch correction it seems that Parseval has made a mistake; there is simply more power in the spectrum.

Basic system model

Now that we have decided how to look at our signals, we need to develop a general layout and strategy for how it will work.

General process summary

First, the signal is“Matricized,”a term we coined to describe our particular algorithm to break up the signal and convert it into the Fourier Domain. Basically, the signal comes in as a long string of sampled values that together represent the whole sound. We, in turn, convert this vector of samples into a matrix for which each column represents the spectrum of one slice, or chunk, of the signal. Although any chunk size could be used, we found the best performance with chunk sizes of 512 samples, which represents about .02 seconds of sound for the 22 kHz sampling rate used on our signals. Next, we take the Discrete Fourier Transform for each of the chunks, showing us the frequencies present at every given moment during the speech. These DFTs are then collected into a matrix with 512 rows and as many columns as there are .02 second long chunks in the voice. With a given chunk, our Harmonic Detection algorithm has the extremely difficult task of accurately and consistently identifying the first harmonic of the voice. With that information in hand, the program reconstructs a new DFT representation for the current chunk by first sliding the first harmonic down the spectrum by the desired shift in pitch, and then following up with all of the other harmonics, shifting each one by an incremental multiple of the first shift. After all of the chunks have been processed and put into a matrix, this new matrix is“Dematricized”in order to convert the information back into the time domain as a new string of digital samples that represent the freshly manipulated voice.

Detailed system model: step-by-step

The pitch synthesizer relies on several algorithms to properly alter the pitch of a person’s voice without mutilating its clarity.

Matricize

First, the signal is“matricized,”a term we coined to represent the task of transforming the string of speech samples into a matrix whose columns each represent the spectrum of an overlapping rectangular window, or chunk, of the signal. Each portion of the voice is contained twice in this information since exactly one half of each chunk is overlapped and contained within an adjacent chunk. Next, each column of the matrix is processed separately, meaning we attempt to change the characteristics of the voice one piece at a time and do so redundantly.

Harmonic detection

Now that we have isolated the spectrum of a chunk of our signal, we use a harmonic detecter to find the first harmonic of the voice at that particular point in time. This task is harder than it first appears and its level of accuracy makes the single biggest contribution to the functionality and accuracy of the pitch synthesizer as a whole. Voiced vowel noises are the only parts of speech that contain pitch, so they need to be processed differently than the rest of the signal. However, since there are many periods of noise as well as voiced (s and z sounds) and unvoiced (like f and t) fricatives alongside these important voiced vowel noises, the harmonic detector must wade through each chunk and first determine whether or not it is dealing with a voiced vowel noise. If so, it computes the index of the first harmonic of the sample by taking the DFT of the first half of the magnitude of the DFT of the original signal chunk. The resulting spectrum will have a very large DC component which represents the grab bag of frequencies present in the original signal, as well as repeating peaks corresponding to the only periodic aspect of the original DFT–the signal’s harmonics. Therefore, the harmonic detector compares the DC amplitude with the next biggest peak, determining simultaneously whether or not this chunk is likely to be a voiced vowel noise and if so the frequency of its first harmonic.

Frequency shift

With this information in hand, our program determines how far each and every frequency must be shifted. Since you interpret the pitch of a voice as the frequency of its first harmonic, the first harmonic is shifted by exactly the desired result. In turn, the frequency of every harmonic is a multiple of the first, so the second harmonic must be shifted twice as far as the first, the third is shifted three times as far, and so on. In fact, we use the index of the first harmonic to determine how much each and every frequency in the original chunk will shift to build up the first half of the DFT for our new, processed chunk. We are trying to alter the pitch without affecting the length of the sound, so this stretched out DFT must be cut off at half the length of the original DFT, at which point we have the completed version of the front half of the new DFT. To complete the second half, we rely on the DFT’s symmetry properties, noting that our original and final sound signals are both purely real. Therefore, the real portion of the DFT is mirrored about the middle, and the imaginary portion is mirrored and flipped. Finally we have completely processed the given window of the original signal.

Reconstruction

To reconstruct the original signal, these processed DFT’s each become a column of another matrix which is then“dematricized”by taking the inverse FFT of each spectrum and placing them side by side into a new signal that has the same length as the original. The only difference of course being that the voice in the signal has become as high or as low as the desired shift.

Pitch shifted speech examples
Unaltered voice Original
Pitch Shifted Voice Up Down

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Speech synthesis. OpenStax CNX. Dec 18, 2004 Download for free at http://cnx.org/content/col10253/1.7
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Speech synthesis' conversation and receive update notifications?

Ask