Return to Main Index for the CDP System.
Return to Spectral Index
1 Output level is the direct result of interpolation
2 Output level follows moment to moment minimum of the 2 infile amplitudes
3 Output level follows moment to moment amplitude of infile1
4 Output level follows moment to moment amplitude of infile2
5 Output level moves, through interpolation, from that of infile1 to that of infile2
6 Output level moves, through interpolation, from that of infile2 to that of infile1
-astart time of startwindow for interpolation, in secs: Default: 0.0
-bend time of endwindow for interpolation, in secs: Default: end_of_file
-csf2 fraction of 2nd sound's frq interpolated at start; (Range: 0 to 1, Default 0)
-def2 fraction of 2nd sound's frq interpolated at end (Default 1)
-esa2 fraction of 2nd sound's amp interpolated at start (Default 0)
-fea2 fraction of 2nd sound's amp interpolated at end (Default 1)
Formerly SPECINTE, this process interpolates between two existing soundfiles. Unlike MORPH MORPH (formerly VOCINTE), this process interpolates between the fixed state of one sound at a specific time in that soundfile, and the fixed state of the 2nd sound at a specific time in that 2nd soundfile. The interpolation only works smoothly with sounds of quite stable spectrum.
You can get an idea of what this means by understanding how the vibrato on a sound can be lost during a BRIDGE process. When a window (fixed state) is taken from the first soundfile, the data is as it were frozen at that point. Then an interpolation takes place simply between the data in the two windows, the two 'frozen' states in each file, not on the data in the first file after the window taken, or on the data in the second file before the window taken. Thus, if there were some vibrato on the first sound after the point at which the window is taken, it is lost.
For more unstable, or noisier sounds, use MORPH MORPH, because this actually works on the data within the time period selected.
Note that there is one time period which applies to both files. During this time period, a transition is made from the 1st to the 2nd sound.
The 6 Modes provide a way to weight the process in favour of the salient features of the soundfiles, and which one you choose to predominate. The process also allows a further degree of weighting of the amount of the 2nd sound's frequency or amplitude interpolated at the start and end of the specified time.
The application here is to move easily between two different sounds, each of which have a steady spectrum. The stability within each sound supports this kind of movement from one sound to the other. Perhaps it can be likened to the kind of smooth aural displacement that takes place when the harmony moves between triads with two notes in common (such as between G-Major and E-minor, E-minor and A-minor, etc.).
The MORPH BRIDGE process is designed to handle movement between sounds which are more (but not too) dissimilar. It takes a great deal of delicate handling to achieve these types of smooth movement between sounds: there is a need to trick the ear at the point of transition analagous to what needs to happen with any harmonic modulation. But in this case, the psycho-acoustics of the process are complex and still very little understood.
The various amplitude following options, for example used with sounds with large variations of amplitude, can be used to combine sounds in remarkable ways.
Also see MORPH MORPH, where there is a somewhat more extended discussion of sound transitions.
End of MORPH BRIDGE
Return to List of functions to morph between
sounds at top of this file
Return to Main Index for the CDP System.
Return to Spectral Index
infile1 and infile2 are single-window analysis files
duration duration of output sound required
We can think of the two grabbed windows as tables of spectral data, a little snapshot cropped from the main source file. The contents will be the frequency and amplitude information for each of the e.g. 1024 channels (whichever value was entered for the number of channels). There will be different spectral data in each of these window-tables.
The data in infile1 becomes the start value, channel by channel, and the data in infile2 becomes the end value, channel by channel. GLIDE creates a linear interpolation between the start and end values, channel by channel, over the duration specified.
Note what a linear interpolation is. Think of a straight line drawn between the start and end values. The number of values and the difference between those values will depend on the duration specified. So we can invoke our visual imagination to create a picture for these two example situations:
1. Widely differing values over a short duration will result in dramatically rising or falling lines.Because the interpolation is linear that is, proceding in equal steps the resulting sound is likely to comprise more or less gradual transitions, which is why GLIDE has been placed in the MORPH category.
2. Scarcely differing values over a long duration will result in very subtle, gradual changes.
Whether rapid and possibly somewhat dramatic, or slow and ever so gradual, MORPH GLIDE provides a way to move between two sounds in a smooth way. But note that the transition is never likely to be as inaudibly smooth as a full spectral interpolation over time as with MORPH MORPH itself. With MORPH GLIDE we should hear and feel the sound being redirected from one state to another. The extremes of the effects possible can therefore be described, perhaps, as a forcible turning on the one hand, and a hardly noticeable translation on the other.
When two timbrally very different windows are grabbed, GLIDE can produce transitions with wonderful timbral modulations.
End of MORPH GLIDE
Return to List of functions to morph between
sounds at top of this file
Return to Main Index for the CDP System.
Return to Spectral Index
1 interpolate linearly (exp = 1),
or over a curve of increasing slope: slow to faster (exp > 1)
or decreasing slope: fast to slower (exp < 1)
2 interpolate over a cosinusoidal spline
infile first of two files to morph
infile2 second of two files to morph
outfile result of the morph
as time in seconds when the amplitude interpolation begins
ae time in seconds when the amplitude interpolation ends
fs time in seconds when the frequency interpolation begins
fe time in seconds when the frequency interpolation ends
The above times refer to time position in the infile, i.e., the first of the two files. expa exponent of the amplitude interpolation
expf exponent of the frequency interpolation
The exponent controls the speed at which the amplitude /frequency interpolation affects the second file, i.e., the rate at which the morph is transfering to the 2nd file
< 1 = it comes in quickly and then the rate of change slows down
1 = it comes in with a linear, steady movement
> 1 = it comes in slowly and then the rate of change speeds up -sstagger time-delay of entry of 2nd file (default is 0.0)
- MORPH MORPH works only with Mono files
- If infile is longer than infile2, the outfile will terminate when infile2 does (infile will be truncated).
- If infile is shorter than infile2, the outfile will continue until the end of infile2.
- If stagger is employed and infile is longer than infile2, the end time of the morph can be stagger plus infile2's duration, but no more.
- If stagger is employed, the start time of the morph interpolation cannot be placed before the entry of infile2: i.e., the start time value cannot be less than the stagger value.
MORPH MORPH is a program which can be used to create smooth aural transitions between different (but fairly similar) sounds. It does this by interpolating between the values in two analysis files generated by PV to analyze the source soundfiles and re-synthesize the outfile of MORPH MORPH. The resulting sound will be a more or less successful interpolation between the two original source sounds.
It is important to understand that the interpolation takes place between the values in the two files while they continue to evolve in time. MORPH interpolates each successive window in the first file with its corresponding (simultaneous) window in the second file, so that the two sounds are continuing to unfold their original morphology during the process of interpolation.
The start and end times for the amplitude and the frequency interpolation can be set separately, and this often needs to be the case to achieve a good morph. Thinking through a morph might involve the following steps:
1. The morph could start at the beginning of each file, or one could listen for a section somewhere in the middle of the files where the spectra are fairly stable. This might be a good place to locate the morph, but ultimately one must try something and listen to the results.
It is possible that these sections do not occur at the same point in each file. Suppose you would like to place the morph between times 2 and 5 in infile (i.e., somewhere in the middle), and between 0 and 3 in infile2 (i.e., at the beginning). To achieve this,
It is therefore possible to lay the two files against each other with considerable variety and precision:
- Set the interpolation start and end times to 2 sec. and 5 sec. respectively – NB: these times relate to the 1st input file.
- Offset the 2nd input file by setting stagger to 2 sec.
- Thus the morph starts at time 2 sec. and ends at time 5 sec. in infile and starts at time 0 sec. and ends at time 3 sec. in infile2.
- You can only offset infile2 and it can start any time before and up to (but not after) the start time of the morph interpolation.
- If stagger sets infile2 to begin before the morph interpolation start time, the morph in infile2 will begin at start - stagger sec. For example, when start = 1.0 and stagger = 0.5, the morphing of infile2 will begin at 1.0 - 0.5 = 0.5 sec. into infile2, and the first 0.5 seconds of infile2 disappears. [I could be wrong about this - AE.]
- If you set stagger to 2 sec. and enter an interpolation start time of 1 sec., it will be rejected, because it comes before the start of the 2nd file.
- no stagger – the beginning of infile lines up with with the beginning of infile2
the morphing begins at the same time point in both files
- stagger = start – the beginning of infile2 lines up with the start of the morph interpolation in infile
the morphing begins at time start in infile and at the beginning of infile2
- infile2 is positioned before start – the beginning of infile2 comes before the start of the morph interpolation in infile
the morphing begins at time start in infile and at time start - stagger in infile2Summary: Thus the stagger parameter can be used to offset the file in which the section to morph comes earlier than the section to morph in the other file – the value of stagger is the amount of time in seconds that it is earlier. Make this file the second input file.
In this way the stagger amount is added at the beginning of the second file (before it starts), such that this file comes into play that much later.
2. Then one considers the amplitude profile of the morph sections. It might be best to match this in time with the frequency components, or start the amplitude change a little before or a little later than the change which occurs in the frequency components.
3. expa and expf can then be used to adjust the changeover between the frequency and amplitude components of the two files. Sometimes both should move in the same way, and sometimes one wants the amplitude change to occur quicker than the frequency change, and v.vs. or in the reverse direction: frequency components might move slowly from the first file to the second, while the amplitude components could move more quickly. This is harder to think through than it seems, because there are in fact 9 different combinations, and of course the range of values > 1 and < 1. The following chart might provide a point of reference:
4. Other considerations:
Shaping Morph Transition Characteristics with the exponent Parameter Example Param exponent Change into 2nd sound 1 amp expa = 1 evenly frq expf = 1 evenly 2 amp expa > 1 slow to faster frq expf > 1 slow to faster 3 amp expa < 1 fast to slower frq expf < 1 fast to slower 4 amp expa > 1 slow to faster frq expf < 1 fast to slower 5 amp expa < 1 fast to slower frq expf > 1 slow to faster 6 amp expa = 1 evenly frq expf > 1 slow to faster 7 amp expa = 1 evenly frq expf < 1 fast to slower 8 amp expa > 1 slow to faster frq expf = 1 evenly 9 amp expa < 1 fast to slower frq expf = 1 evenly
- What if the two files are at different pitch levels? Try cutting out the morphing section of one of the files, creating a time-varying transposition (probably in the spectral domain) to the level of the other file and replacing it before doing the morph.
- What if one file is pulsed and the other isn't? Try extracting the amplitude envelope of the pulsed one and imposing it on the other file before doing the morph. (See ENVEL EXTRACT and ENVEL IMPOSE).
- What if one of the files has such a variable spectrum that it interferes with the smoothness of the morph? Try a time varying spectral BLUR starting at the point where the morph is to begin.
- What if the two sounds have distinctly different formant components? Try extracting the formants from one of the sounds and imposing them on the other.
We are now familiar with the practice of gradual shape transformations between visual images. The process has a wonderful surprise value as the first image seems to alter before our very eyes, becoming another quite different image, such as a face becoming that of another person.
You may also possibly have observed that just at the moment of transition, the first image begins to melt or distort in some way. I say 'possibly' because it tends to happen very quickly, and because our eyes/brain tend to construct a familiar image, it's rather difficult to notice what happens inbetween. However, it is very instructive to do so. If it didn't change in some way before the second image made its presence felt, there would in fact not be a transition, just an abrupt change. This is the principle of 'modulation' in action.
which is precisely where we need to turn our attention when seeking to carry out an audio-morph. Modulation in music has been used up till now to move from one tonal region to another, and you will recall how it is common practice to begin by dissolving the identity of the existing tonal region, such as by using tonally ambigous diminished 7th harmonies.
The idea of creating surprise and astonishment by causing one sound to become another is in itself easy to grasp. What's not so easy is making this smooth to the point of being almost imperceptible. Herein lies the art of the morph, and once again the concept of modulation is relevant. ('Morph', by the way, is a Greek word meaning 'form'.) This program gives a taste of the morphing process. The CDP spectral domain programs provide many other processes that can be used to 'pre-process' sounds to achieve a more psycho-acoustically effective transition.
Here, the best results will be achieved by using sounds which are already quite similar.
Historical note
MORPH is derived from VOCINTE, which was originally written at IRCAM
during the composition of VOX-5. I would like to thank the many people
there who offered me help and advice. I would also like to thank
Andrew Bentley who modified the first versions of the program to work
with the (Atari-based) CDP soundfile system and to operate more
efficiently.
(Trevor Wishart)
End of MORPH MORPH
Return to List of functions to morph between
sounds at top of this file
Return to Main Index for the CDP System.
Return to Spectral Index
Aplogies - This section is not yet completed.
1. Encapsulating these three morphing methods.
2. Some of the other functions which might be called upon to assist with the audio-deception of the morph. (stretching, time-varying transposition, imposing formants/spectral envelopes or time-domain envelopes from one of the sounds to the other (before the morph), time-varying blurring ...
3. Additional comments on the glossary item: Linear interpolation. Two words to be clear about. First of all, an interpolation can ... linear means equally spaced values. The steps between each value become smaller when there are more and more divisions to be made between the start and end values. ...
End of Technical Discussion
Return to List of functions to morph between
sounds at top of this file
Return to Main Index for the CDP System.
Return to Spectral Index