Simple Examples

It is best to learn how to use this program by working through numerous examples. You can run these examples by running scribe and loading one of the indicated project files.

The key problem in transcribing or annotating an audio file is finding the the melody in the spectrogram. For music played on a solo music which plays only one note at a time (as opposed to a guitar or piano), the problem is easy. For example, consider the home made recording drowsy.wav. The spectrogram is very simple and can be annotated automatically with good success. Here is how the spectrogram looks, using an fft size of 512.

Note the text line "loaded audio file examples/..." that appears at the bottom of the window. This area often contains important messages and hints.

It is now a good idea to play around with the program and try different settings. Click on the cfg menu button and select the spectrum radio button. Try the different FFT sizes. The next image shows the same spectrogram using a 1024 FFT.

The analysis window size depends upon the the FFT size, which affects the tradeoff between frequency and temporal resolution. When you increase the FFT size you may find it necessary to also adjust the brightness and contrast levels. When working with more difficult material, you will find all of these controls essential to getting the best visual representation of the information of interest.

Now switch from the spectrogram to midigram representation using the top menu button. The display should now look something like below.

You may find it necessary to adjust the vertical scrolling. You will find the midigram appears more complicated due to the presence of the many partials. The first partial is double the frequency of the fundamental, so it appears one octave higher. The next partial is triple the frequency of the fundamental so it appears one octave plus a fifth higher. To hear the pitch associated with each tone position the mouse pointer over one of the horizontal bars in the midigram or spectrogram and press the space bar. You should hear a short beep corresponding to that pitch and a purple horizontal line will appear temporarily at this pitch. To hear the original press the right mouse button without moving the mouse pointer.

You can also view the correlogram, however, it is less meaningful and harder to interpret in this application. If you wish to see the spectrum and autocorrelation functions at a specific time, first set the cursor (vertical red line) at the time of interest by left clicking once in the spectrogram/midigram/ or correlogram. Be careful not to drag the cursor while pressing the button or else you will select a region. Now press the key `u' on the keyboard. Two additional windows will pop up with graphs. There are various controls in these windows that you can play with.

Note that occasionally, you will see an error message, FFT window out of bounds. Just click OK (one or more times) and carry on. This message indicates that you had not selected a start time (with the vertical red cursor), before pressing u. You will find that the spectrums and autocorrelation functions are automatically updated any time you move the cursor. Be careful not to move the cursor over those plots or else you will see other error messages. The program is still more of a research tool rather than a turnkey system. You can close these two windows, since they are not needed at this point.

Now for practice, you should try to annotate the spectrogram so that it looks something like this.

To do this, you use the mouse pointer, the space bar and `g' key on your keyboard using this procedure. Place the mouse pointer over the bar at about one second and 0.7 kHz and press the space bar. You should see a horizontal purple line going through this bar. If it is too high or too low just adjust the position of the mouse cursor and press the space bar again. When it is finally at the right pitch, you need to specify the time and duration of the note by dragging the mouse while holding the mouse button button. The following image, shows how the screen may look like.

Now press the g key on your keyboard, and that note will be grabbed.

After grabbing a small sequence of notes as was illustrated, you are ready to play them on a MIDI synthesizer. To do this merely press the `m' key on your keyboard while the mouse pointer is positioned anywhere in the spectrogram window.

(If you do not hear the MIDI representation but instead see an error message like "couldn't execute timidity", you will need to do some configuration. Timidity is a free midi player available for many platforms. It is usually installed in most new Linux operating systems. For Microsoft Windows, you can substitute the media player which is found in various places depending on the version of your operating system. (To find it, you need to find it in the start/ programs /accessories list and determine its properties.) For Windows PC, it is strongly recommended that you use Winamp (available from winamp.com) as your intermediary for playing MIDI files. Once you have located and tested an application for playing MIDI files, you must tell this program in one of two ways. The easiest way manner is to go to the cfg menu button and select miscellaneous. Now using the browse button, find the midi file player and open it. The other way is to edit the file scribe.ini and replace the path the desired executable for the variable `player'.)

You may hear a few wrong notes. You can adjust the pitch of the note by selecting the note using the mouse pointer. It should appear in green and now adjust it up or down using the up and down keys on your keyboard. The `d' key will delete this note, the + and - keys will lengthen and shorten the note. The left and right arrow keys will move the note.

The MIDI file may not be played on the instrument of your preference. To change it, you should click the cfg button and select the notation radio button on the top. Now press the `midi program' button and select the desired instrument. The slider on the left, allows you to adjust the volume level (velocity) to use in creating the MIDI file.

Now we shall try a few other interesting experiments. To start load the project file drowsy.prj. This will load a fairly complete annotation of this file. You can hear the entire annotation by pressing the 'M' key. You have probably heard a couple of out of tune notes. Now go to the auxiliary menu and select pitch plot. The following plot should be placed on your screen.

This plot shows the pitches of the notes as measured from your annotation onto a grid. The grid lines correspond to the correct frequencies of the notes assuming a 440 Hz tuning for the key of A. It is apparent that the tuning of this recording is quite far off which explains why some of the notes are off. The program allows you to change the tuning by resampling the file. This was described in the scribe.html documentation in the htmldoc directory. You will find this feature useful in a lot of your work.

The reason why some of the notes are out of tune is because the program quantizes the pitch to the nearest MIDI note. Some notes may be rounded up and others rounded down which may introduce a semitone error (flat or sharp). You can manually correct these notes using the edit features described above. When you select a note (i.e. appears as a green bar), there is an annotation along the bottom line of the window which tells you the pitch in midi units and the corresponding key. The fourth note should be D instead of D#. You can lower it using the down arrow until the annotation specifies the correct note. The note will not appear exactly over the black bar in the spectrogram, but this is unavoidable in this situation.

This file is one of the rare examples where you can use the program's autograb feature available from the auxiliary menu. If there are any note annotations, in your window remove them by pressing the `E' (for erase). Now open the autograb window accessible from the auxilliary menu. Press go. The program should automatically find all the notes withen the frequency range specified by the two sliders. This completes the discussion for this audio file, however, we shall return to it later when we discuss the tools for converting the MIDI representation to music notation.

Now let us move on the file geambaseasca.wav recording geambaseasca.wav. The spectrogram which contains a short excerpt from a Romanian dance call Geambaseasca de la Tortomanu.

In this example, you hear a solo clarinet accompanied by various string instruments. It is not too difficult to find the clarinet signal in the spectrogram; however, the tempo is a lot faster and it is necessary to zoom into a smaller time segment to see the details. In this example, we also use a shorter window (FFT size = 512) so that the temporal details do not get smeared. After a few adjustments the spectrogram image looks like the following.

The autograb function could be used to identify most of the notes, but I found it necessary to edit some notes manually in order to get a reasonable representation. If you load the file geambaseasca.prj, you can see and hear my interpretation. It was found useful to slow the music down by a factor of 2 by adjusting the rate parameter in the programs menu. This also slows down the playback of the MIDI file generated by the program.) This file also illustrates another feature of scribe. When you play the file, you also hear a bass accompaniment. These were also notated, but you must switch to track b in the cfg/notation menu. The track a annotations will become invisible but the other annotations will now appear.

Before giving you some exercises to try, there are a couple of common problems that you should be aware.

Things to beware

2) Though the start position is indicated by a vertical cursor, the program only plays a few milliseconds when you click on the play button. You probably dragged the mouse cursor slightly specifying a small area. Erase the dragged area by double clicking and try specifying the start point again.

3) The frequency resolution of the program seems inadequate even though the largest FFT size window was selected. The sampling rate of your file is probably 44100 Hz or larger. The program runs best if you resample it to 11025 Hz or around that.

4) When increasing the frequency resolution and expanding the vertical scale, the spectrogram has a salt and pepper appearance. The canvas height is probably inadequate for the spectral resolution you are using. Go to the cfg/spectrum menu and increase the canvas height by a factor of 2 by entering the new size in the entry box. The spectrogram should have a smoother appearance.

More difficult examples

The next example, zagroski.wav. the matching tones technique is a lot more difficult to apply. This is part of a Croatian dance called Zagrosky Drmesi.

The problem is that the melody is carried by a sequence of chords making it more difficult to pick out the pitch. None of the notes in the chord seem to stand out visually. Nevertheless they are all there; load the project file zagrosky.prj for the solution.

The situation is very similar for the vocal section of the the Croatian song. It is not too clear whether it is better to view the spectrogram at a resolution of 1024 or 512. Ajdza Milim Ajdza Dragim.

As a hint, the vocalists sing in the range of 300 to 500 Hz.

Creating a Music Transcription

All timing information are recorded in MIDI pulse units, where the number of pulses per second depends on the tempo of the music. In order to convert the MIDI file to music notation it is necessary to know the length of a quarter note in units of MIDI pulses. The header of the file contains a variable called PPQN (pulses per quarter note) for this purpose. The time signature by default is assumed to be 4/4, however the MIDI standard provides a means of indicating the time signature in the tempo meta command. In order for scribe to provide the correct information it is necessary for you indicate the beat of the music by inserting bar lines.

To illustrate the general process, we return to the simple tune Drowsy Maggie. To save some time load the project file drowsy.prj into scribe.

First go to the cfg/notation configuration page and change the number of quarter notes per bar to 4, the bar divider to 3, and time signature to 4/4. The configuration page should look like below.

Now to place bar lines on the screen, position the mouse cursor to the position of the first bar line and press the key `b'. Next use the F3,and F4 to adjust the bar line spacing. If you hold the control key down, the bar line spacing will change faster. Make fine positioning adjustments using the F1 and F2 keys. The dashed vertical bar lines indicate the positions of the bar lines while the dotted vertical lines divide the bar into quarter notes. If you load the project file drowsy2.prj, scribe should be configured correctly. Finally press the key `a', and you should see the message scribe.abc was created at the bottom of the screen. (If you instead get an error message like "couldn't execute midi2abc no such file or directory" then you may have to indicate in the cfg/miscellaneous configuration window the correct path to midi2abc.exe.) In any case, scribe will generate a MIDI file called scribe.mid independently whether it also created scribe.abc. The MIDI file should be found in the scribe folder or wherever the scribe program was executed from.

If you have created scribe.abc, you can view it using any text editor since it is a regular text file. This is an abc format music notation file for which there are some free notation programs. If you do not have your own music notation software, then you can download various programs from sourceforge.net. When you convert the MIDI file to `common music notation' you should get something similar to.