Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Bullshit wins v. science
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Date: Fri, 8 Nov 2002 08:13:22 -0000
NNTP-Posting-Date: Fri, 08 Nov 2002 08:13:23 GMT
"N. Thornton" wrote in message
> "Kevin Aylward" wrote in message
> > "N. Thornton" wrote in message
> > > John Woodgate wrote in message
> > > > about 'Bullshit wins v. science', on Wed, 6 Nov 2002:
> re speaker distortion due to resonance.
> > > > The resonances (one or more) of these systems do not involve any
> > non-
> > > > linearity at all, so no non-linearity distortion is produced.
> > > It is still distortion, since the audio output does not accurately
> > > follow the electrical input.
> > Ho humm. No it isnt, as used by *any* *pro* ee in standard techical
> > descriptions.
> > Yes, it could be argued that technically, distortion means any
> > from v0(t)=C+ A.vin(t) equals. However, no one does this.
> > distortion *means* non-linear distortion, i.e. THD, or IMD.
> Distortion means, and I quote:
> "The state of being distorted, or twisted out of shape or out of true
> position; crookedness; perversion."
> That is the _meaning_ of it.
Your pissing in the wind. An engineering definition of distortion is not
the same as an English language definition of distortion. Try looking up
the definition of an "Observable" in Quantum Mechanics, e.g. Hermitian
> The approach and industry practice you describe for measuring
> distortion only measure certain types of distortion. They do not
> _define_ distortion.
In practice it does. Its what is meant by using the term distortion,
unqualified. For example if someone was referring to phase aberrations,
on would have said "phase distortion".
The issue here is that you are simply not conversant with standard
> Lets take a really clear example to illustrate. Lets say you delay
> your audio signal by 1 second twice, and add the 3 signals: the
> original one, the 1 sec delayed one, and the 2 sec delayed one. Any
> speech put through that would be unintelligible. According to the
> _definition_ of distortion, it is indeed distorted, badly distorted.
> But if you measure the THD of this distorting process, it is zero.
In fact if had taken probably any course on this in university, for
example, it would have been pointed out that delay distortion is not
usually refered to as "distortion".
> I am perfectly aware that THD is the usual figure used, and am also
> aware that it does not, contrary to popular ignorance, give a proper
> picture of a speaker's distortion.
It gives a proper indication of its non-linear amplitude distortion, as
understood by anyone knowledgeable in the field. There is no contrary to
popular ignorance on this matter at all. Only ignorance concerning what
standard terminology really means by novices. THD has never implied
anything about what the frequency response of a speaker is.
>A little thought will soon show why
Indeed it would.
> they don't quote the _real_ distortion figure, it would be far worse,
> and not as simple to test.
You still pissing in the wind. Give it up. You wont change the
establishment one little bit.
Frequency response variations are called the frequency response of the
system, and this is indeed specified for speakers. A decent data sheet
will contain graphs of *both* distortion and frequency response, and
both are quite easy to test. It would confuse things no end to refer to
frequency response as distortion.
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