to Spectral Index
outfile is a binary formant file, which can be used in other formant applications
infile an analysis file
outfile a binary formant file
-f extract formant envelope 'linear frequency-wise', using 1 point for every N equally-spaced frequency-channels
-p extract formant envelope 'linear pitchwise', using N equally-spaced pitch-bands per octave
This is a straightforward utility to extract and store the evolving spectral envelope of a sound. In earlier CDP systems it was called SPECFGET.
On Extracting Formants
The two extraction options (-fN | -pN) relate to resolution. Essential information: the logarithmic nature of the pitch scale means that as one goes higher, an increasingly wider band of frequencies is encompassed by the 'octave'. The octave of a tone is double that tone's frequency. Thus the octave between 220Hz and 440Hz encompasses 220Hz, while the octave between 2200Hz and 4400Hz encompasses 2200Hz.
- -fN 'linear frequency-wise' is an 'equal spacing' comprising equal differences.
- -pN 'linear pitchwise' is an 'equal spacing' comprising equal ratios.
With 'linear frequency-wise', the analysis channels define frequency bands of identical bandwidth: each band will encompass the same frequency range.
With 'linear pitchwise', the frequency bands actually get wider as one goes higher. For example, if linear pitchwise is set at N = 12, the octave between 220Hz and 440 Hz is divided into 12 semitones; if N = 3, the octave is divided into 4 minor thirds (each of slightly increasing bandwidth). In the octave between 2200Hz and 4400Hz these same divisions will consist in considerably wider bandwidths. In other words, linear pitchwise is working via ratios with the logarithmic relationship of pitches.
Linear frequency-wise should therefore be chosen if the main formant area of interest is in the higher frequencies, because there will be better resolution here when extracting the spectral envelope. But if the main interest in the sound is in the lower frequencies, then the linear pitchwise option will be suitable: the frequency bandwidths relate to the octave bandwidths. You are also able more easily to think in terms of normal musical terminology for intervals. If in doubt, you'll need to experiment.
Linear frequency-wise and linear pitchwise Linear frequency-wise Linear pitchwise 'Equal' means: frequency spacing is the same N = 2 octave divisor is the same N = 12 E.g., band is 220Hz 86Hz (e.g,) encompassed by every 2 channels 12 semitones within that octave E.g., band is 2200Hz exactly the same bandwidth 12 semitones within that octave Recommended application better resolution with higher frequencies effective with lower frequencies
The nature of the source, we should also observe, affects the results.
Formant extraction and preservation is therefore a difficult process and ideal results are not obtained in every case.
- With a noisy source, there is energy all over the signal. It is therefore easy to find the envelope of the source and extract the formants.
- With a pitched source, especially a high voice, there will be just a few partials with significant energy and, although these lie under the formant envelope, there is often not enough data to get a good indication of where the whole formant is.
- A sonogram is not really the best way to identify formants, says Richard Dobson. Better would be a per frame FFT-style display of amplitude/frequency along with a display of the spectral envelope. The Snack-based sonogram display available in Sound Loom does not have a facility for selecting a frequency band directly from it. We would recommend Audacity for inspecting the spectrum of a sound and picking out a formant region.
- We are currently exploring peak tracking and ConstQ Pvoc as ways to improve pitched partials and formants extraction.
- For more detailed information and a software option, please see Prosoniq .
This process is essential when wanting to preseve the timbral qualities of a sound. They can be transferred to another sound, or they may be re-imposed on the original sound after it has undergone some other transformations. The re-imposing is done with FORMANTS PUT.
infile an analysis file
outsndfile a pseudo-soundfile ready for viewing. Do not resynthesize or play this (an error message will be returned).
-fN extract formant envelope linear frequency-wise, using 1 point for every N equally-spaced frequency-channels
-pN extract formant envelope linear pitchwise, using N equally-spaced pitch-bands per octave
-s semitone bands for display (Default: equal Hz bands)
The resulting logarithmically scaled display indicates formant shapes, but NOT the absolute amplitude values.
See a detailed discussion of the two extraction options in the text for FORMANTS GET for further information on this choice.
Previously a part of SPECFSEE, this process produces a pseudo soundfile which can be viewed in the same way as a normal soundfile. In the display we see a series of spectral windows, separated by zeroes. The horizontal display represents the spectral frequencies and this may be displayed in a manner which increases regularly with frequency (linear frequency-wise) or in a manner which increases regularly with pitch (linear pitch-wise). The vertical display represents the amplitude of each spectral band. The range of amplitudes is very large indeed, and in order to display them in the soundfile format, the log of the amplitude values is used and scaled to utilise fully the range of sound-sample values (-32768 to 32767).
The display therefore indicates only the shape of the spectrum, and how that shape changes through time - no absolute amplitude values can be read off from it.
FORMNTS GETSEE uses linear interpolation in determining the spectral contour. The output pseudo-soundfile is viewed by loading it into a soundfile display program, such as CDP's VIEWSF.
SPECIAL NOTE It is important to realise that the output 'soundfile' is in this case a 'pseudo-soundfile'. All pseudo-soundfiles and binary files are displayed by DIRSF, and on PC are automatically given a .wav extension. It is therefore recommended that you adopt a naming convention that indicates which type of file it is, such as 'fmnt...' for the formant file produced by FORMANTS GET, 'psnd...' for the output of GETSEE, and 'bpdf...' for the binary pitch data file produced by PITCH. The different types of file all have their own 'property strings' written in the header, so the system will know what they are and prevent inappropriate use; the naming conventions are for your own convenience.
When a program produces a textfile, it is NOT given a .wav extension and will not be displayed by DIRSF. Look for textfiles in the current directory, with the command 'dir'.
outfile is an analysis file ready for resynthesis
1 New formant envelope REPLACES the sound's own formant envelope
2 New formant envelope is IMPOSED ON TOP OF the sound's own formant envelope
infile and outfile PVOC analysis files
fmntfile a formant data file made with FORMANTS GET
-llof lof = low frequency, below which spectrum is set to zero
-hhif hif = high frequency, above which spectrum is set to zero
-ggain gain = adjustment to spectrum loudness (normally < 1.0)
-i quicksearch for formants (less accurate)
Previously SPECFPUT, FORMANTS PUT reads a spectral trajectory as stored in formant file and imposes it on infile. In many sounds, the amplitude peaks are focused around certain frequencies; these are called formant areas, and are a key factor in creating the timbral colouration of a sound. These formants may themselves change over time, forming a spectral trajectory. The spectral trajectory is extracted (prior to running FORMANTS PUT) with FORMANTS GET. This trajectory (i.e., spectral envelope) is the rising and falling amplitude pattern of the partials (frequencies).
When this pattern is imposed on another file, the precise spectral envelope changes ­ and colourations ­ are introduced into the receiving file.
The presence of the spectral trajectory data in the fmntfile makes it possible to impose the same data on more than one file.
There are several musical purposes which can be achieved with this process:
- simply as a means to link/unify musical data
- to re-colour a sound with the timbral characteristics of another
- to give one sound the meanings associated with another sound (this applies especially to recognisable sounds from the world around us)
infile a binary formant data file created with FORMANTS GET
outsndfile a 'pseudo-soundfile' suitable for display in a graphic soundfile editor (do not resynthesize or play (an error message will be returned)
-v display data about formant-band parameters
The resulting logarithmically scaled display indicates formant shapes, but not the absolute amplitude values. This process used to form a part of the CDP program SPECFSEE. In the display we see a series of spectral windows, separated by zeroes. The horizontal display represents the spectral frequencies and this may be displayed in a manner which increases regularly with frequency (if linear frequency-wise was selected when using FORMANTS GET) or in a manner which increases regularly with pitch (if linear pitch-wise was selected).
The vertical display represents the amplitude of each spectral band. The range of amplitudes is very large indeed, and in order to display them in the soundfile format, the log of the amplitude value is used and scaled to utilise fully the range of sound-sample values (-32768 to 32767).
infile and infile2 analysis files
outfile resultant analysis file
-fN extract formant envelope linear frequency-wise, using 1 point for every N equally spaced frequency channels
-pN extract formant envelope linear pitchwise, using N equally-spaced pitch-bands per octave
-llof lof is low frquency, below which data is filtered out
-hhif hif is high frquency, above which data is filtered out
-ggain gain is the amplitude adjustment to the signal (normally < 1.0)
FORMANTS VOCODE achieves 'cross-synthesis'; it was formerly called SPECVOCO, but here has been re-written extensively.
Cross-synthesis takes the time-evolving spectral envelope of one sound and imposes it on another sound. For example, vocal shouts will have a strong spectral profile. If this is imposed onto the sound of running water, we should hear the water shout.
Strictly speaking, this is not 'morphing', which is more of a gradual transition from one sound to another. But in a broader sense, it certainly is the reshaping of one sound with the characteristics of another.
The difference between frequency-wise and pitch-wise could be important. As discussed in FORMANTS GET above, linear frequency-wise divides into absolutely equal frequency bands, while linear pitchwise divides octaves (of varying frequency widths) into equal-ratio bands, but these bands will vary in size from octave to octave, wider as one goes higher. It was recommended above to use frequency-wise if the sound is concentrated in the higher frequency areas (to get better resolution), and pitchwise for lower frequency areas. Experimentation is still the name of the game.
Frequencies below lof and above hif are simply ignored when the new spectrum is reconstructed.
Gain is not predictable because it depends on the level of the signals you put in, their relative levels, and the way those levels are distributed over the spectrum. A process that boosts level a great deal at the low end of the spectrum can cause distortion. Try it with no gain first.
Resonance is the transmission of vibrations from one vibrating body to another. A resonator is a body which reacts with sounds of any frequency or pitch, such as the sounding body of a piano or the belly and back of a violin, or the cavities associated with the vocal tract.
The effect of a resonator is to amplify certain frequency regions. These regions remain constant, unless the shape of the resonator is altered. Whatever partials are present in one of these regions will be amplified. The result is a perceptibly similar tone colour (timbre), even when the fundamental pitch of the vibrations is changing.
The human voice provides one of the best examples of this phenomenon. The vowels produced by the human voice maintain a constant 'oo' or 'ah' while the fundamental pitch changes, as long as the shape of the mouth etc. remains constant: the same frequency regions are amplified even though the pitch is going up or down. The specific formant (frequency regions) associated with each vowel have been identified and can be used to impose a given vowel sound onto any other sound.
A formant, then, is an absolute frequency region in which the (changing) partials contained in any given sound are amplified, resulting in a constant timbre amidst changing pitches.
While this phenomenon occurs naturally through resonance effects, formants can also be produced on the computer by boosting the amplitudes of the partials in the specific frequency regions associated with a given vowel or tone.
The spectral envelope is the shape made by the amplitude levels of the partials contained in a sound. Note that this is not a fixed shape lasting throughout the duration of the sound. Rather, which partials are present at any given moment (i.e., the spectrum) and the amplitude level of these partials is changing all the time. Some sounds are very steady, with not so much change, while other sounds are constantly changing a great deal. The latter tend to be the more useful sounds for a variety of spectral manipulations: there is simply more to work with.
Also see the more detailed discussions and examples in: