|
To amplify Eric's comment:
Since V3.44, there is even a new opcode (lpinterpol) that should let you
interpolate filter coefficient of two analysis and apply the resulting
filter to any other sound. By doing the cited method, you will have a
volume interpolation between sound filtered with filter1 and sound filtered
with filter2. Using lpinterpol, you should get a filter sweep between the
two settings.
Marc.
PS: If anybody gave it a try, I would be glad to hear any feedback about
its usability...
:
: To amplify Jean Piche's comment:
:
: Csound already has tools that are in some ways superior to the Morpheus.
: If one concatenates two different sounds in one soundfile, uses lpanal
: to analyze the file and create two data frames, then one can use an
lpread/
: lpreson pair (along with balance) to interpolate between the two. Filters
: in the 6 to 14 pole range are easy and usually quite stable. Above twenty
: poles you have to make certain that the poles are all inside the unit
circle
: (or really increase the k-rate and trust in balance) but you can do 40
poles
: if you realy want to. If the original soundfile had three sounds, you
could
: "morph" among three sounds and so forth.
:
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Date: Sat, 01 Mar 1997 23:43:13 +0000
To: csound@maths.ex.ac.uk
From: Richard Wentk
Subject: Re: Morphing
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At 07:47 28/02/97 -0500, you wrote:
>> Can anyone point me in the direction of technical books or papers on
>> the subject of morphing audio signals?
>
>
>Not to reopen this can of worms, but I have seen very little serious
>litterature on audio morphing. There was considerable debate a while
>back about this, on this list and elsewhere. One can can effectively
>argue that morphing two audio signals is very similar to simply mixing
>them. Interpolating two fft analysis files on a bin-to-bin basis over a
>period of time would, in theory, be close to the well-known analogous
>process in computer graphics/animation, but in my experience, the
>results of this process in audio is almost identical to conventional
>linear mixing. Which is to say that other more complex operations
>(stretching, compressing, transposing etc.) on a pair of
>frequency-domain data blocks have much more interesting sonic potential.
>The term "morphing" is the problem here.
I use the Composer's Desktop Project software which includes tools that do
this, and in my experience the idea that you can simply interpolate between
FFTs and get a morph to sound convincing is naive. And I disagree that a
morph is the same as a crossfade. A true morph would create a half-way
stage that is neither one sound or the other but includes characteristics
of both. A cross-fade doesn't do this.
The problem with the FFT is that it's looking at this problem the wrong
way. When you identify a sound you don't hear it as an FFT, but as a
combination of pitch, amplitude envelope, short-term timbral detail, and
medium-term timbral envelope. To create an acceptable morph you have to be
able to isolate these factors and control them individually. This is
moderately easy for monophonic sounds but spectacularly difficult for
polyphonic sounds.
In short, to create a convincing morph between sounds that are dissimilar
you have to model the sounds and interpolate the coefficients of the model
from one sound to the other. Which model you use - LPC, physical modelling,
some variant of the FFT that adds extra information about pitch and timbral
envelope, or whatever - doesn't matter as much as the ability to describe
the sounds convincingly at each end of the morph and change the model's
coefficients smoothly.
If you do this you can get some very interesting results, particularly with
short morphs that mutate a single monophonic sound quite quickly. But it's
a long and tedious process, and requires a lot of trial and error before
you find something that works well. For some sounds, especially those with
a very variable amplitude envelope, you can get very good results by simply
copying the envelope variation from one sound to another and doing a
crossfade 'under' the new envelope. For other sounds the process is a lot
more complicated...
R.
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Date: Sat, 1 Mar 1997 21:02:26 -0500 (EST)
From: Lawrence Troxler
To: csound@maths.ex.ac.uk
Subject: Re: Morphing
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> > Interpolating two fft analysis files on a bin-to-bin basis over a
> >period of time would, in theory, be close to the well-known analogous
> >process in computer graphics/animation, but in my experience, the
> >results of this process in audio is almost identical to conventional
> > mixing
Actually, isn't linear mixing *absolutely* identical to interpolating
between FFT frames, since addition in the frequency domain equals
addition in the time domain?? Forgive me if I'm missing something.
-- Larry Troxler -- lt@westnet.com -- Patterson, NY USA --
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From: Tobias Kunze
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In-Reply-To: Richard Wentk "Re: Morphing" (Mar 1, 11:43pm)
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To: Richard Wentk , csound@maths.ex.ac.uk
Subject: Re: Morphing
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| To create an acceptable morph you have to be able to
| isolate these factors and control them individually. This
| is moderately easy for monophonic sounds but spectacularly
| difficult for polyphonic sounds.
Problem is, that `morphing', as Jean Piche pointed out, is
not a technical term. In fact, it wouldn't really denote
anything at all, wouldn't its ethymology suggest some sort
of treatment of something's `morphology'. In other words,
the concept is intuitive, but its realization is not.
Surely, for some processing to be called a true `morph',
you'd have to have a handle on every psychoacoustically
important feature of the signal. But you won't be able to
get that from any known DSP technique. Even more, if you
look close enough, `morphing' doesn't even work in graphics.
Typically, you'll see two images "approach" each other
through a more or less boring, brownish and blurry swamp of
intermediary states.
The general problem here is that the salient features you
think you're interpolating in the straightest manner
imaginable, will inevitably engage in unforeseeable complex,
interesting and distracting interactions (to counteract the
noisy intermediary states, composers have always spent the
extra effort of actually inventing and carefully shaping
each state--as opposed to applying a mechanism).
I think one can not meaningfully combine `morphing' and
`signal processing' in any single sentence. Except in the
preceding one, of course ;)
--
______________________________________________________________________
Tobias Kunze t@kunze.stanford.edu
CCRMA, Stanford University http://www.stanford.edu/~tkunze
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From: rasmus ekman
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Subject: Re: Morphing
References: <59003B5D25@beethoven.music.qub.ac.uk>
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So, there is a lot to say. But what to do? One technical difference
between "morphing" and "mixing" is this. _If_ you have two sounds
with a clear formant structure (spectral peaks), the mix would
simply fade out one formant structure and fade up the other,
whereas the "morph" would move the spectral peaks from one profile
to the other. How to do this is not always clear. And whether it
sounds convincing is another question. Trevor Wishart has done a
lot of work from a perceptual and practical point of view. His
writings may not be "technical", but they do spell out several of
the issues involved. Try to get hold of his "On Sonic Art", or
maybe better, the more recent "Audible Design". There are several
sections on these and related topics. Both come with example
tape/cd (and both are privately published, not?). Also, his work
"Tongues of Fire" is largely a showcase for this way of thinking
about music (transformative).
Try this URL until you get hold of any of these texts:
http://web.interval.com/~malcolm/AudioMorphing/
It's a brief text, but it mentions some issues, and it does have
a few more references.
cheers,
re
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From: Marc Resibois
To: Csound List
Subject: Curve equation needed...
Date: Sun, 2 Mar 1997 11:27:11 -0000
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Hi everybody,
I'm looking for a particular parametrical curve who could fit the following
scheme: Imagine a unity square defined by the two following points
(0,0)-(1,1). For a given value of the parameter (let's say zero), the curve
would be the diagonal of the square. When the parameter would augment, it
would slowly distord in order to map the upper half border of the square [
i.e. defined by (0,0)-(0,1)-(1,1) ]. Ideally, when the parameter is
inifinite, the curve would exactly map this contour.
Does such a curve exist ? I'm pretty sure it does but I don't know where I
should look for this information.
Many thanks for any hints,
Marc.
|