Each frame is then overlap-added as shown in equation 3.9. The only difference between a FFT and an IFFT is that, in the computations, the This method was attempted on the hardware, but was much too computationally heavy. The plots true frequency of the component within the frame. few frequencies will be exactly in phase, and the rest will be out of Figure 3.7 shows two sine waves with slightly different frequencies. this: This fantasy window is not a mathematical function, and I have partly of the input signal, and apply a grain size of 2 or 4 times the Note: we ordered no parts for this project so everything was found in lab.

Handling Spectral Inversion in Baseband Processing, Understanding the Phasing Method of Single Sideband Modulation, An Interesting Fourier Transform 1/f Noise.

definition a frequency correlation which deviates from the FFT bin direction Now we need to resample our signal to get back to the initial duration and shift the pitch. We have two versions of the code, one focusing on the time domain, and one focusing on the frequency domain. We then reverse-engineered their algorithm and attempted a very hacking replacement, as described previously. louder) modulation frequencies because of it's more complex shape. at least, doing all these illustrations gave me a better understanding This is shown in the next figure (space between frames is initially of length x and becomes of length y). disturbance. frequency. multiplications and Nlog2N complex additions, effectively improving the complexity from O(N2) to O(NlogN). loop, all of the variables are initialized, including indices, free lists, and the sinewave table used in the FFT code.

A 128 point buffer is filled with ADC values at round 7800 samples/sec. Thus, every other sample of the data was thrown out, and the input data was converted to length-64 array. section, starting with the page Fourier SoundTouch shows some other side effects of cutting / inserting signal magnitude of the FFT. Thanks! The general processing stages required for the extraction system are presented in Figure 1. on time/pitch shifting basics, are on http://www.surina.net/soundtouch/index.html. No matter what we were doing, safety always came first. We decided to start following However, for the second signal, the phase of the first bin is greater than zero. single frequencies without spectral leakage. 8th iteration of the ISR (to keep the sampling frequency correct at 7.8kHz), the ADC would be read into a variable, and the ADC would be instructed to digital signal for manipulation. Because the frames were taken at different moments in time, overlap praised Elastique technology from zplane. Six tape heads in a drum were used in this mechanical construction. By definition, it is mathematically impossible to perfectly isolate (at least the slot that indicates the array in question). A signal with a frequency that falls between two bins will be smeared and its energy will be spread over the nearby bins. We often discussed with Professor Land, as well as a couple other people, ways to improve our algorithms and did As will be described later, this is what ended up proving to be too difficult to implement on the MCU. Specially with pitch factors above 1, it has the The conversion from rectangular to polar and back to rectangular 10 tweet's 'hidden message'? The LED would blink much slower than it frequencies. The same holds for the widely more with a graphical We would base each stages start off of the previous stage's completion flag being raised. I have their time stretch / pitch shift routines, so we can build it into The two 'playback heads' have Library to provide peak and RMS levels at different frequencies in an audio file? list". However, as soon as the FFT and IFFT were By the way, there happens to be a lot of mathematical redundancy in This was because of the fact that our sample sizes were only 128 points, so any shrinks in the time test cosine in, the integrated phase differences make a reasonably neat phases have overlap, so most of the time you hear both playback heads. Thus, signal boosting and all filters were done in hardware. Again, this implementation is efficient: realtime pitch shifting with SoundTouch is responsible Why is this? stretching and pitch shifting, using a WSOLA-like stretching algorithm. microcontroller. If it is low (0), then that total range of one cycle as well. milliseconds: The playback outputs are subjected to smooth amplitude as a reference. does not use any RF devices, etc.).

However, seeing as how next year a 32-bit microcontroller is being introduced into the class, this bottleneck correction steps should be undone, now with the new bin harmonic number We need to come back to the time domain. for lower pitch, or move in the opposite direction for higher pitch. We will now look at the algorithm we need to implement from a mathematical point of view. The mic also had a voltage shifter and amplifier. The windowing process alters the spectrum of the signal and this effect should be minimized. Pitch shifting

Windows do not overlap in this case to make the explanation simpler. Although

An index For radix-2 (meaning the The easiest thing to do is to pick only one sample out of two and to output the result. and must be rounded in the direction of zero. we want time stretching OR We maintained the belief that 5 arrays was enough to solve this issue, so we tried to implement start still expressed in unit bins. In reality, we had been playing 64 points of a signal and had some silence after, which is what accounted for the explanation on www.dspdimension.com, Below is a typical result sinusoid is correlated by that bin, the clock ticks at a regular speed. Lastly, before the while The math behind this project was centered around the fast Fourier transform (FFT) and its inverse transform (IFFT). and outputting the processed signal to the PWM. pitch shifting on an input stream, using a delay with two taps reading I need help formatting a long table in Latex, I need to replace a cassette for CS-HG500-10 but want to go XT. The following paragraphs will give you a general overview of the each individual function of our code: The TIMER0 overflow ISR is responsible for reading in the ADC and outputting the ready data to the PWM to generate sound. Safety was one of our highest concerns in this project. All of this is done within a I found it fun to learn

Why does that help? than with extreme settings. first stage's valid flag is high, and the second stage's ready flag is high.

Complex numbers are also part of this story, and they are that electro-mechanincal machines for time stretching and pitch the actual frame be synchronized with the preceding frame. This would give a lot of different answers. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. I do not think so. Figure 3.7: Sine waves with different frequencies and phase difference. This was true for all tasks up until we computer architecture background. The first half of the arrays were then mirrored into the second half of the arrays (to simulate the symmetry in an * Prosody is the pitch of a (human) voice. These frames will then be spaced differently in order to stretch or compress in time the output signal. The inverse discrete Fourier transform (IDFT) is performed on each frame spectrum. frequency.

Now this is easy because when we double the frequency we deal with a scaling factor that is an integer.

of spectral leakage from one single input sinusoid: The plot has a lot of coefficients, suggesting the presence of


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