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This module discuss the process of analyzing an audio signal for music transcription.

The method of music transcription: analyzing the signal

Distinguishing between notes

Our second module (get_note) is the one that will analyze the signal at a specific time, split the signal into the different notes, and get the frequencies of each note. Since each element of the matrix corresponds to a magnitude, the frequency with the maximum magnitude at a specific time instant represents the frequency of the signal at that time. Therefore, we need to check the maximum magnitude for every column and determine the frequency. Sometimes, however, some columns will not have a frequency because no note is being played ag that time instant, but it will still have a maximum magnitude at a frequency because it has noise. To deal with this, we have set a threshold magnitude that determines whether a column has a note to be analyzed or not. If the maximum magnitude at a column is below the threshold, the frequency at that time will not be considered a note, therefore it will not be analyzed.

To identify a note, we use simple edge detectors. When the signal changes frequency, the program will analyze each column until it detects another change in frequency. The range of time instants obtained from this process will represent a single note, and the frequency of the note will be the average of the maximum amplitude frequencies of each time instant in the given range. Each frequency of each note will be inputted to the identify_note module one at a time for it to output the note name. To prevent any imperfections, we have also created a time threshold, such that, if the length of a note (time instants between edge detections) is lower, such note will not be analyzed because it will not be considered a note.

NOTE: The frequency and duration thresholds work together to distinguish between notes and noise. There may be a few consecutive time instants for which noise is greater that the amplitude threshold. However, no signal should have noise that is consistently greater than the amplitude threshold for the duration of the duration threshold or longer. As such the two thresholds work in tandem to eliminate notes from the transcription process.

NOTE: The duration threshold does involve a tradeoff: while noise is eliminated, the user is prevented from analyzing a file that contains notes that are less than 100 time instants long. Any such note would be treated as noise. As such, the program may be unable to correctly handle very fast rhythms in low quality signals.

Identifying notes

Our next module will basically identify the note. It takes a frequency as an input and it outputs a string with the name of the note being played. We have created a library with different frequency ranges that correspond to different notes. The module will find the range to which the input frequency corresponds and input output the string for that range. This process will be done for every note that is given by the get_note module.

This identification process would not be possible if we only had a regular spectrogram, since the precision is very low, causing a very high error that would lead to wrong identification of a note. The frequency reassignment process is an extremely essential part of this method.

Generating synthetic audio files

As an extra module, we have created a simple function to create tones, in order to test our project. In this function, we have different square waves with different frequencies. We simply create a vector with the notes that we want and we have a song to be analyzed.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
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Source:  OpenStax, Elec 301 projects fall 2011. OpenStax CNX. Jun 18, 2012 Download for free at http://cnx.org/content/col11431/1.1
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