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https://github.com/billthefarmer/ctuner

Musical instrument strobe tuner
https://github.com/billthefarmer/ctuner

tuner

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Musical instrument strobe tuner

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# Musical instrument strobe tuner ![.github/workflows/build.yml](https://github.com/billthefarmer/ctuner/workflows/.github/workflows/build.yml/badge.svg)



A musical instrument strobe tuner with cents and frequency

display. With additional features useful for tuning accordions or

melodeons. The strobe display may be replaced with the staff, if

required. Windows and [Mac](swift) versions are available. An

[Android](https://github.com/billthefarmer/tuner) version is

available, also on

[F-Droid](https://f-droid.org/packages/org.billthefarmer.tuner).



|     |     |

| --- | --- |

| ![Tuner](https://github.com/billthefarmer/billthefarmer.github.io/raw/master/images/ctuner/Tuner.png) | ![Options](https://github.com/billthefarmer/billthefarmer.github.io/raw/master/images/ctuner/Options.png) |

|     | ![Filters](https://github.com/billthefarmer/billthefarmer.github.io/raw/master/images/ctuner/Filters.png) |



## Using



Play your instrument into your microphone and observe the

display. The slider at the top left adjusts the microphone input

level, the oscilloscope display at the top shows the input

waveform. The display below shows the spectrum of the input. It

may be zoomed in and out by clicking on the pane. When zoomed in

the display shows about ±50 cents around the current note and

includes all concurrent notes within that range.



The numeric display shows the note, deviation in cents, correct

frequency, actual frequency, reference and frequency

deviation. The display may be locked by clicking on the pane. The

displayed values may be copied to the clipboard for pasting into

another application by typing Ctrl-C. The strobe display below

shifts left or right according to whether the input note is flat

or sharp. It may be turned off by clicking on the pane. The meter

below shows the deviation in cents. The Options button pops up

the Options window, the Quit button quits the application. The

status bar shows the sample rate and the correction.



## Options



The zoom and strobe tick boxes may be used to turn the zoom and

strobe display off and on. The Filter tick box controls a

3dB/octave audio filter on the input. This is intended to make it

easier to tune low notes by reducing the level of harmonics. The

downsample tick box controls a downsampling algorithm that

enhanced the fundamental frequency in the input. It also

generates spurious subharmonics that should be ignored. The

display lock tick box may be used to lock the display. The resize

tickbox may be used to resize the display. The multiple tickbox

may be used to display multiple sets of values. The slider below

and the + and - buttons allow the reference to be adjusted.



Some audio input devices appear to have inaccurate clocks. Out of

three laptops I have tested, two were up to 0.7% out. The

correction facility allows a correction factor to be entered. The

value will not be remembered until the save button is clicked. A

known standard may be used to set this value. For example, my

netbook has a correction value of 0.99322. The done button

dismisses the window.



## Keyboard shortcuts



  * All the options may be changed by pressing keys, they are:

    * C, Ctrl-C - Copy values to clipboard

    * D - Switch downsampling on and off

    * F - Switch filter off and on

    * K - Change strobe colours

    * L - Lock display

    * M - Display multiple sets of values

    * O - Pop up Options dialog

    * R - Resize display

    * S - Switch strobe display off and on

    * T - Display multiple sets of values

    * Z - Zoom spectrum display

    * + - Expand spectrum display

    * − - Contract spectrum display



## How it works



I have included a How It Works section because none of the other

open source tuners that I have looked at give any explanation of

the algorithms used. This tuner uses an overlapped Fast Fourier

Transform together with the phase difference between sequential

runs of the FFT to measure the actual frequency accurately. It

appears to be about as accurate as the clock in the sound

card. The filter is a single pole Butterworth filter with a

corner frequency of 120Hz. The output of the FFT is scanned by a

peak detector which detects up to eight peaks in the

spectrum. The highest peak is taken as the measured note, other

peaks are shown on the zoomed in spectrum if within range, all of

them are displayed if the multiple option is on.