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Explains the process used to pitch match words for use with the speak and sing.

Introduction

Pitch correction of the human voice is a common activity, with applications in music, entertainment, and law. It can be used to alter pitch to produce a more accurate or more pleasing tone in music, as well as add distortion effects. Several programs for entertainment use a form of pitch correction to modulate and distort a user's voice, allowing one to sound like a different gender or emulate a celebrity or other well-known voice. Voice distortion is also often required to protect the anonymity of individuals in the criminal justice system. However, it is the first of these applications that we are most interested in - producing a pleasing, tone-accurate song from a human voice.

Implementation

Pitch adjustment of a digitally-sampled audio file can be implemented simply using resampling. However, this completely alters the time scaling and cannot account for changes in the pitch and inflection of a voice over time, and thus cannot be considered. Instead, we shall use the more sophisticated Pitch-Synchronous Overlap Add algorithm, which allows us to modify pitch without compromised information or modifying the time scaling.

The pitch correction method involves the following basic steps:

  • Detection of original pitch
  • Parsing of desired pitch frequencies
  • Correction of pitch

Pitch detection

First, the pitch of the original signal is determined. This is done using the FAST-Autocorrelation algorithm. This algorithm makes use of the fact that for a signal to have pitch, it must have a somewhat periodic nature, even if it is not a strictly periodic wave. The signal is divided into several small windows, each only a few milliseconds long and containing thousands of samples - enough to detect at least two periods and thus to determine the window's frequency.

Finding periods

Each windowed segment is autocorrelated with itself to identify the length of the period. This is done by convolving the signal with itself with an increasing offset τ to obtain the autocorrelation function:

R(τ) = f(-τ) * f(τ)

For discrete, finite-length signals, it can be found as a sum of the product of the signal and its offset, in this form:

R(s) = Sum(x(n)x(n-s))

This autocorrelation acts as a match filter: the signal and its offset form will be the most alike when offset s is equal to one period. Thus, the autocorrelation function is at a minimum when the offset corresponds to the length of one period, in samples.

Making it fast

Autocorrelation in this fashion is very computationally expensive - one can expect that the algorithm will have to convolve two length-1000 signals several hundred times for each window to obtain the frequency from within the full possible range of frequencies for a human voice. To speed this up, we can make two assumptions:

  1. The frequency of a window should be relatively close to that of the window before it
  2. The first minimum corresponds to the period, so no further minima are needed

By starting at an offset relatively close to the previously found period length (perhaps 20 samples before where the period was found), we can eliminate a few hundred calculations per window. If a minimum is not found in this area, we simply broaden our range and try again. To reduce the computation time further, we also calculate the derivative dR(s)/ds to determine where the minimum occurs. Once we find the first minimum, we are finished with obtaining the frequency for this window, having shaved off up to 70% of our computation time.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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Source:  OpenStax, Speak and sing. OpenStax CNX. Dec 21, 2009 Download for free at http://cnx.org/content/col11151/1.1
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