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The solution we came up with to alleviate this problem is to average what the program thinks is the highest frequencies across multiple frames of data. We tested out different average lengths and found that averaging every 25 frames sounded the best. Our code will keep track of a variable-length list that contains the frequency of the highest peak per frame. At the start of every frame a new frequency value will be added to the list, and at the end of every frame the list is averaged to determine a single frequency. This list resets every 25 frames. In midst of this process, we also converted to linear frequency from FFT bins, which is done by multiplying by the ratio of the sampling frequency over half the chunk length. To further improve our results, we only added to the list frequencies if the magnitude of that particular frequency bin is above a particular value. This way our code will ignore the low amplitude noise and only record frequencies when a note is being played.

flag = 0 freq = []while(True): data = stream.read(CHUNK)x = numpy.fromstring(data, dtype=numpy.float32) x_filtered = scipy.signal.lfilter(taps, 1.0, x)X = numpy.fft.fft(x_filtered) highest_freq = numpy.argmax(abs(X[0:511]))flag +=1 if (X[highest_freq]>5000): freq.append(highest_freq*44100/(CHUNK/2))avg = (sum(freq)/len(freq)) if flag == 25:flag = 0freq = []

Creating the harmony

Once we have the correct frequency and the identity of the note, we proceed to figure out the frequency of the harmonizing note. We first create a Python dictionary of musical keys mapped to a list of the corresponding frequencies of that note at different octaves. For purposes of demonstration, we only added the key of C to the dictionary. However, other keys could easily be added. We then created a function that helps on determine which harmonic we are in given a musical key and the frequency of a note. We then apply the formula for finding the harmonizing frequencies describe in the previous section to the frequency we have and obtain the frequency of the third and fifth intervals from the note being played.

keys = {'c':[1636,1636/2,1636/4,1636/8]}sBuf = 50 def key_select(freq, key):for f in keys[key]:if freq>= f: return freturn freq def chord_freqs(key, note):n = 1200*numpy.log2(note/key) if(500-sBuf<= n<=500+sBuf or 700-sBuf<= n<=700+sBuf or n<=sBuf): f3 = note * math.pow(2, (400)/1200)f5 = note * math.pow(2, (700)/1200) return f3 , f5elif (200-sBuf<n<200+sBuf or 400-sBuf<n<400+sBuf or 900-sBuf<n<900+sBuf): f3 = note * math.pow(2, (300)/1200)f5 = note * math.pow(2, (700)/1200) return f3, f5elif (1100-sBuf<n<1100+sBuf): f3 = note * math.pow(2, (300)/1200)f5 = note * math.pow(2, (600)/1200) return f3, f5else: return 0,0

After obtaining the two harmony frequencies, we tried to take them into the time domain. We initially tried add triangles of frequency content centered at the desired frequencies and then taking the inverse transform, in hope to try to mimic a "real" sound. However, doing that caused the note to sound slightly off. Also we didn't add imaginary components to the frequency and the FFT library gave us warnings. So we decided to try out other approaches. The next thing we thought of was using the Karplus-Strong Plucked String algorithm to create a realistic decaying note. But we very quickly saw that the algorithm was not really meant to be used in real time. The algorithm works by creating the complete decaying signal. However, this is problem with other stream because we can only output 1024 samples at a time, which is not long enough to squeeze the whole decay in. We thought about storing the whole signal from the Plucked String algorithm and output it a frame at a time. But doing so not only slow down our system, but also would introduce problems if we played a different note half way through a output decaying note. We ended up deciding to just output pure sine waves and worry about making it sound less synthesized in the future.

def play_tone(stream, frequency=252, length=1, rate=44100): chunks = []f3 , f5 = chord_freqs(key_select(frequency, 'c'), frequency) chunks.append(sine(f3, length, rate)+sine(f5, length, rate))chunk = numpy.concatenate(chunks) * 0.25 stream.write(chunk.astype(numpy.float32).tostring(), CHUNK)def sine(frequency, length, rate): length = int(length * rate)factor = float(frequency) * (numpy.pi * 2) / rate return numpy.sin(numpy.arange(length) * factor)

Now that we were only outputting pure sine waves, we decided that it would be faster and save computation complexity but just creating the sine waves of the correct frequencies in the time domain directly. This would save computation time as now we don't need to compute an inverse FFT. To put it all together. We output the harmonies through the PyAudio stream. The UCA222 takes this and adds it to the guitar signal that it is already forwarding to the speakers.

Questions & Answers

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
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
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
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
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
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
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Source:  OpenStax, Harmonizing guitar pre-amp. OpenStax CNX. Dec 15, 2015 Download for free at http://legacy.cnx.org/content/col11932/1.4
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