The Tuners




Juan Coria


Sergio de la Cruz


Noe Villa

Objective

A clear and practical application for the frequency approximation device is the tuning of a piano. By using the device, it will be easier to determine the frequency of the strings on a piano. The device to be developed will accept a signal from a piano, process it, and determine it's frequency with variable range. An algorithm named the Phase Interpolation Estimation (PIE) will be used to estimate the frequency of any input signal received by the device. The function of the device will be to approximate a single tone, within noise using the PIE algorithm.

Abstract

A clear and practical application for the frequency approximation device is the tuning of a piano. By using the device, it will be easier to determine the frequency of the strings on a piano. The device to be developed will accept a signal from a piano, process it, and determine it's frequency with variable range. An algorithm named the Phase Interpolation Estimation (PIE) will be used to estimate the frequency of any input signal received by the device. The function of the device will be to approximate a single tone, within noise using the PIE algorithm. Digital signal processing has many diverse forms and applications in today's information technology driven world. Since there are several types of information sources, there are also several types of methods to receive, control, and employ this information. This project will deal with the problem that arises from interpreting and manipulating tonal information. However, it will do so in a manner that will not use conventional methods, such as the prony and Pisarenko algorithms. The tonal information that will be used to input a signal in the device will come from musical instruments. The musical instruments of choice for this device include, but are not limited to, the piano, guitar, violin, cello, and trumpet. A clear practical application for the frequency approximation device is the tuning of a piano. By using the device, it will be easier to determine the frequency of the strings on a piano.

Method of Completion

The preliminary design consists of a step-by-step progression through a system that will convert the input signal, a tone, to a displayed output, on a computer monitor, which will be an approximation of this signal. In order to do this, the signal must be received by means of a microphone connected to a pre-amplifier circuit that will magnify the signal enough for the next stage to be able to interpret it. The pre-amplifier (pre-amp) is the next component in the circuit for accepting the signal from the piano. The piano will be the input source that will be taken in by a Sony Dynamic Range Microphone. Once the microphone has accepted and interpreted the signal from the piano key, it will then be transferred to the pre-amp. The subsequent step, which will consist of an Analog to Digital (A/D) converter, will sample the signal fed to the following stage where the frequency will be estimated. The processing chip will take the digitized input signal and will put it through the PIE algorithm. The A/D converter will receive the analog input signal and return a digital version of it. The core of the signal analysis will be done in the DSP by implementing the PIE algorithm. The algorithm will take the input signal and will perform a series of mathematical manipulations on it to estimate the signal's frequency. A LabView interface will serve as a medium for communication between the DSP and the computer monitor. After the signal has been compared and filtered for noise, the chip will then send the result of the approximation to a GUI (Graphical User Interface) that will show the frequency of the input signal in Hertz. The GUI will interpret the frequency, obtained through the DSP, and will provide the signals necessary to display this frequency on a computer monitor.

Issues

The accurate estimation of the frequencies of sinusoidal tones embedded in noise is a problem encountered in many diverse fields, e.g., radar, sonar, geophysics, and radio astronomy. The main problem in this project will be to implement an efficient method to receive an input signal from a piano in the form of sound and determine its frequency by using different methods than the ones already available. Along with the above-mentioned problem, the issue of dealing with noise in the input signal will also have to be addressed. Since accuracy will be of the utmost importance in the project, the noise issue will have to be resolved. The project will approach the problems described above in a very unique way. A device will be developed that will accept a tonal signal from a piano, process it, and determine its frequency with variable range. An algorithm will be used to estimate the frequency of any input signal received by the device. The algorithm is fairly new and employs approximation techniques to determine a frequency, hence the unique approach. The main function of the device will be to approximate a single tone, within noise, from the phases of Discrete Fourier Transforms (DFTs). D.R.A McMahon and R.F. Barrett developed this approach (5) in 1985, and their technique will be the source for the algorithm used in the project.

Schematics



Conclusion:

The display for the frequency will be shown on a computer monitor instead of an LCD display. The computer monitor will contain a GUI that will dispaly the frequency. An LCD (Liquid Crystal Display) could not be used, due to the fact that the communication between the BASIC STAMP and DSK could not be achieved due to the internal clocks in the DSK and BASIC STAMP. The clock in both components could not be synchronized. A GUI intefrace, especially developed for the TMS320C5402, was used instead to give a display of the frequency for a piano or guitar.