On Fri, 31 Mar 2006 15:25:24 +0100, Nick Gorham
wrote:

Don Pearce wrote:

All sound can be treated as though it is composed of sine waves.


All sound can be treated as if its composed of putty, but that still
doesn't mean that it is.

Dealing with waves only in the frequency domain does mean you have lost
temperal (phase) information.


And how exactly do you think that a cable might screw this up? And do
bear in mind that the speaker itself subsequently does a heroic job of
doing exactly that.

d

Pearce Consulting
http://www.pearce.uk.com

And what exactly makes you think I was suggesting it would, Don't assume
what side of the fence I am on this one.

I was just replying to the assumption that a FFT gives you ALL the
information about a signal, and the deeper assumption that just because
a model is useful, then the model is equivalent to the reality.

But an FFT DOES give you all the information - phase as well as
frequency. THe fact that the normal presentation of the data is simply
a magnitude plot is neither here nor there.

THe FFT is not, though, as you say, a model of reality. It is a model
of what reality would look like if it were repeated for ever - it
should have the word Groundhog in there somewhere. Provided you
understand the depths of it, though, it is a very useful tool that can
do virtually anything an audio engineer would want of it.

d

Pearce Consulting
http://www.pearce.uk.com

In article , Nick Gorham
wrote:
wrote:
Glenn Richards wrote:

Dave xxxx wrote:

All sound can be treated as though it is composed of sine waves.


All sound can be treated as if its composed of putty, but that still
doesn't mean that it is.

Indeed. Hard to see that such a 'treatment' would make much sense...
Although it may have its uses for Handel's "Water Music". :-)

Dealing with waves only in the frequency domain does mean you have lost
temperal (phase) information.

Not so. :-) You simply define the phase of each frequency component as
well as its amplitude. It then follows from the standard maths methods of
'Orthogonality' that any real signal pattern (i.e. finite amplitude,
duration, and bandwidth) can be fully represented as a series of sinusoidal
components. Indeed, Information Theory relies on this. :-)

There may be some similar maths behind 'putty theory', but if I was taught
about it, it didn't stick... ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Nick Gorham
wrote:
Don Pearce wrote:



Dealing with waves only in the frequency domain does mean you have
lost temperal (phase) information.


And how exactly do you think that a cable might screw this up? And do
bear in mind that the speaker itself subsequently does a heroic job of
doing exactly that.

d

Pearce Consulting http://www.pearce.uk.com

And what exactly makes you think I was suggesting it would, Don't assume
what side of the fence I am on this one.

I was just replying to the assumption that a FFT gives you ALL the
information about a signal, and the deeper assumption that just because
a model is useful, then the model is equivalent to the reality.

Alas, what you said is incorrect. Please see earlier posting.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Don Pearce
wrote:


But an FFT DOES give you all the information - phase as well as
frequency. THe fact that the normal presentation of the data is simply a
magnitude plot is neither here nor there.

It seems common to plot 'power' versus 'frequency', but in theory all an FT
or FFT does is gives you a method to transform information from one form
into another, nominally with no loss at all. People then may choose to
discard the phase info if they so wish, but the transform can provide it.

THe FFT is not, though, as you say, a model of reality. It is a model of
what reality would look like if it were repeated for ever - it should
have the word Groundhog in there somewhere.

Actually *an* FFT (since there are various processes which can be called
such) is a computational method that returns the same transformation as an
FT. The advantage is computational speed. The snag is source code that may
cause some head-scratching, and makes finding some typos a nightmare. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Fri, 31 Mar 2006 16:23:33 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:


But an FFT DOES give you all the information - phase as well as
frequency. THe fact that the normal presentation of the data is simply a
magnitude plot is neither here nor there.

It seems common to plot 'power' versus 'frequency', but in theory all an FT
or FFT does is gives you a method to transform information from one form
into another, nominally with no loss at all. People then may choose to
discard the phase info if they so wish, but the transform can provide it.

It is just as well that phase information is preserved; if it weren't,
then reversing the procedure back into the frequency domain would
result in an unrecognizable signal.

THe FFT is not, though, as you say, a model of reality. It is a model of
what reality would look like if it were repeated for ever - it should
have the word Groundhog in there somewhere.

Actually *an* FFT (since there are various processes which can be called
such) is a computational method that returns the same transformation as an
FT. The advantage is computational speed. The snag is source code that may
cause some head-scratching, and makes finding some typos a nightmare. :-)

FFT, DFT - whatever. As long as the number of calculations doesn't
increase exponentially with the number of points, It'll do for me. The
central looped core of an FFT is fairly small, though - not too much
trouble to debug. Just don't use an in-place algorithm.

d

Pearce Consulting
http://www.pearce.uk.com

Don Pearce wrote:
On Fri, 31 Mar 2006 16:23:33 +0100, Jim Lesurf
wrote:


In article , Don Pearce
wrote:



But an FFT DOES give you all the information - phase as well as
frequency. THe fact that the normal presentation of the data is simply a
magnitude plot is neither here nor there.

It seems common to plot 'power' versus 'frequency', but in theory all an FT
or FFT does is gives you a method to transform information from one form
into another, nominally with no loss at all. People then may choose to
discard the phase info if they so wish, but the transform can provide it.


It is just as well that phase information is preserved; if it weren't,
then reversing the procedure back into the frequency domain would
result in an unrecognizable signal.


THe FFT is not, though, as you say, a model of reality. It is a model of
what reality would look like if it were repeated for ever - it should
have the word Groundhog in there somewhere.

Actually *an* FFT (since there are various processes which can be called
such) is a computational method that returns the same transformation as an
FT. The advantage is computational speed. The snag is source code that may
cause some head-scratching, and makes finding some typos a nightmare. :-)


FFT, DFT - whatever. As long as the number of calculations doesn't
increase exponentially with the number of points, It'll do for me. The
central looped core of an FFT is fairly small, though - not too much
trouble to debug. Just don't use an in-place algorithm.


Ok, I stand corrected :-)

Actually I have spent much more time dealing with DCT than anyhing else.

What I notice a lot and Jim may be able to explain this, is the HiFi
mags seem to often do FR plots using what they describe as a convolved
inpulse analysis, I have a theory what this means, but it would be nice
to have some references (ok, so I guess I could just look it up).

Its mainly through playing with RIAA stages that I have become aware of
the importance of maintaining phase as well as frequency response, but
maybe this is old hat for you pro's.

--
Nick

On Fri, 31 Mar 2006 17:07:23 +0100, Nick Gorham
wrote:

Don Pearce wrote:
On Fri, 31 Mar 2006 16:23:33 +0100, Jim Lesurf
wrote:


In article , Don Pearce
wrote:



But an FFT DOES give you all the information - phase as well as
frequency. THe fact that the normal presentation of the data is simply a
magnitude plot is neither here nor there.

It seems common to plot 'power' versus 'frequency', but in theory all an FT
or FFT does is gives you a method to transform information from one form
into another, nominally with no loss at all. People then may choose to
discard the phase info if they so wish, but the transform can provide it.


It is just as well that phase information is preserved; if it weren't,
then reversing the procedure back into the frequency domain would
result in an unrecognizable signal.


THe FFT is not, though, as you say, a model of reality. It is a model of
what reality would look like if it were repeated for ever - it should
have the word Groundhog in there somewhere.

Actually *an* FFT (since there are various processes which can be called
such) is a computational method that returns the same transformation as an
FT. The advantage is computational speed. The snag is source code that may
cause some head-scratching, and makes finding some typos a nightmare. :-)


FFT, DFT - whatever. As long as the number of calculations doesn't
increase exponentially with the number of points, It'll do for me. The
central looped core of an FFT is fairly small, though - not too much
trouble to debug. Just don't use an in-place algorithm.


Ok, I stand corrected :-)

Actually I have spent much more time dealing with DCT than anyhing else.

What I notice a lot and Jim may be able to explain this, is the HiFi
mags seem to often do FR plots using what they describe as a convolved
inpulse analysis, I have a theory what this means, but it would be nice
to have some references (ok, so I guess I could just look it up).

Its mainly through playing with RIAA stages that I have become aware of
the importance of maintaining phase as well as frequency response, but
maybe this is old hat for you pro's.

The thing about impulse analysis is that it results in something that
is visually very easy to understand. Convolution is just a
mathematical trick for subjecting a signal to some sort of
fequency-dependent transformation. Roughly speaking, convolution of a
signal and a response in the time domain is equivalent to FFTing them
both into the frequency domain, multiplying them together
point-by-point and then re-FFTing them back to the time domain.

As for things like RIAA correction, it uses what is called a minimum
phase response. What this means is that each amplitude value has a
unique and unambiguous phase associated with it. In practice, what
this means is that you don't have to worry about it. Get the amplitude
right, and the phase will follow.

d

Pearce Consulting
http://www.pearce.uk.com

In article ,
Glenn Richards wrote:
Dave xxxx wrote:

if you believe in him you will be telling us you can hear speaker
cables differences lol

Actually, a lot of agnostics and atheists can hear speaker cable
differences. There's no hocus-pocus involved, just some science that the
sceptics disregard.

The science is called psychology and it's called "The emperor's new
clothes syndrome"

--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

On Fri, 31 Mar 2006 14:55:34 +0100, Nick Gorham
wrote:

wrote:
Glenn Richards wrote:

Dave xxxx wrote:


if you believe in him you will be telling us you can hear speaker
cables differences lol

Actually, a lot of agnostics and atheists can hear speaker cable
differences. There's no hocus-pocus involved, just some science that the
sceptics disregard.

So, you can send a sine wave down a bit of cable and it'll come out the
other end as exactly the same sine wave. Guess what? Music isn't a sine
wave.


All sound can be treated as though it is composed of sine waves.


All sound can be treated as if its composed of putty, but that still
doesn't mean that it is.

Dealing with waves only in the frequency domain does mean you have lost
temperal (phase) information.

Sampling techniques such as PCM digital audio accurately maintain all
phase relationships within the frequency band of interest, they do not
operate only in the frequency domain.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
----------------------------------------------------------
http://www.usenet.com

On Fri, 31 Mar 2006 17:07:23 +0100, Nick Gorham
wrote:

Its mainly through playing with RIAA stages that I have become aware of
the importance of maintaining phase as well as frequency response, but
maybe this is old hat for you pro's.

The *vast* majority of RIAA stages are of minimum phase design, so
that if you have the amplitude response correct, then the phase
response *must* be correct.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Posted Via Usenet.com Premium Usenet Newsgroup Services
----------------------------------------------------------
** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
----------------------------------------------------------
http://www.usenet.com