Ceres Help

If you have any comments on Ceres, send a mail to

oyvindha@notam.uio.no (Øyvind Hammer).

Introduction

Ceres is a simple program for displaying sonograms and for sound effects in the frequency domain.

Ceres is started simply with the command "ceres". You may give an FFT size parameter as a command-line parameter (for advanced users!). An empty window will appear with a menu bar at the top.

Select "Load & Analyze" in the "File" menu, and select a sound file. There is unfortunately no way to change the default directory "/sounds". Ceres accepts files in AIFF or AIFC format, any sampling rate, mono or stereo (stereo files will be treated as mono).

The file will then undergo a phase vocoder FFT analysis with N=1024, and the analysis will be stored in memory. This means that there is a limit on the size of the sound file, because the analysis data size will be huge. If the program crashes for sounds shorter than 30 seconds at 44.1 kHz sampling frequency, your computer has a too small swap space anyway, and your swap space should be increased. A sonogram is drawn as the analysis progresses.

At any time, you may change the color map of the display in the "Settings->Display" dialogue.

You may now use the options in the "Transform" menu to change the spectral data, as described below.

To hear the result, you must resynthesize the sound with the "Synth & Save" button in the "File" menu, and then play the sound either with the "Play" option or with the "sfplay" command in your UNIX shell. Sorry 'bout the directories and file names not updating in the Play file selector.

In the "Settings->Resynthesis" dialogue, you may control the way the sound is resynthesized. "Resynth time stretch" does what it says, but the result may have irritating pulsation in it. To avoid this, and to avoid a "gritty" sound that may result from some transforms, select "Additive synthesis". This will select an additive synthesis method instead of inverse FFT.

3. Transforms

Many of the transform parameters can be controlled over time using a control function. Select "Settings->Display->Show control function" to display a breakpoint curve which can be edited using the middle mouse button (press Backspace or Delete to remove a node).

Using the right mouse button, you may select a rectangular area in the spectrum. Consecutive transforms and exports will then only apply to this area.

Sieve

Sieve is a useful operation which will only retain the N strongest frequency components for each analysis window. This makes an interesting sound in itself for N less than about 20, and it can be used as an effective noise reduction method for larger N. Also, it is often necessary to reduce the amount of data with "Sieve" before you export the analysis to a Csound score file (see below).

You may select any N ("Number of harmonics"). This value N may be multiplied continuously by a factor which you select for exponential increase (A>1) or decrease (A<1). A=0.5 will thus apply an envelope in such a way that N is halved each second. This is great for "morphing", because you can let one sound "desintegrate" and another "integrate", and then mix the two together. You can also control N from the control function by ticking the box.

A composer here wanted more "life in the top", and so you can weight high frequencies with the "Boost" parameter. Try the value 1.

The "Probability" field gives the probability (0-1) that a given frequency component at a given point in time will be moved to the nearest frequency in the grid.

Convolve

Convolve is an experimental function which is probably of little use. You may select different standard convolution operators (3X3 masks) used in digital image processing.

4. Export

The Export functions let you send analysis data to text files for later processing in other programs.

Parmerud Csound scorefile

This specialized export was made for the Swedish composer Aake Parmerud. The frequency axis is divided into a number of "strings". As soon as the amplitude in a frequency band corresponding to a string exceeds the Trigger value, a new Csound note is written with a duration given by the Resonance value. After a number of seconds (Hysteresis), the string will again enter a trigger mode, waiting for the amplitude to exeed the threshold.

Spectral peaks

Writes all spectral peaks as time-amplitude-frequency triples.

Csound scorefile

Sends the complete spectral analysis to a Csound score file. Each line represents a "pixel" as shown in the sonogram, and is formatted as follows:

i1 Starting_time Duration Frequency Amplitude

Note that "Duration" will always have the same value.

Warning! The Csound score file may become ***huge***. It is strongly recommended to do a Sieve operation first, to reduce the number of non-zero pixels.