On Wed, 7 Feb 2007 17:20:28 +0200, "Iain Churches"
wrote:

As an ex-patriot, I am probably often far more patriotic than
someone actually living in the UK. (Maybe distance lends
enchantment to the view:-)

The situation here in Scandinavia is much more healthy, it seems
to me.

In Sweden, everyone who knows anything at all about audio
can tell you about Per Johansson and the Swedish group of
researchers and experts from the renowned German Fraunhofer
Institute, who invented MP3.

Any Finn, who knows anything about audio is justly proud of
the achievements of Matti Otala, the man who first realised the
significance of intermodulation distortion in audio amps in 1973


ITYM transient intermodulation distorion; plain old IM had been known
about for decades.

His achievement was only significant in terms of publicity. TIM was
just another name for clipping inside the loop due to poor design and
was, AIUI, understood by competent designers well before Mr Otala
produced his obfuscations.

Present at this conference was Svein Erik Børja, a Norwegian record
and broadcasting producer, and a great audio enthusiast.
Svein Erik Børja was one of the most famous of the Golden Ears
breed. He took part in a large number of both sighted an non-sighted
tests, and had a remarkable ability to detect linear imperfections of
a very low order in audio amplifiers. He had been deeply dissatisfied
with the sound of transistorised audio, and the lecture given by
Dr. Otala about TIM also was an explanation to Svein Erik for
the imperfections he himself had noted in audio amplifiers.

The Danes too have a long tradition in audio design, with many fine
products. Lyrec, B+K etc etc.

We British have been undervaluing our products and
achievements for so long that people are starting to believe us:-)


Iain

Bill Taylor wrote:
On Wed, 7 Feb 2007 17:20:28 +0200, "Iain Churches"
wrote:

As an ex-patriot, I am probably often far more patriotic than
someone actually living in the UK. (Maybe distance lends
enchantment to the view:-)

The situation here in Scandinavia is much more healthy, it seems
to me.

In Sweden, everyone who knows anything at all about audio
can tell you about Per Johansson and the Swedish group of
researchers and experts from the renowned German Fraunhofer
Institute, who invented MP3.

Any Finn, who knows anything about audio is justly proud of
the achievements of Matti Otala, the man who first realised the
significance of intermodulation distortion in audio amps in 1973


ITYM transient intermodulation distorion; plain old IM had been known
about for decades.

His achievement was only significant in terms of publicity. TIM was
just another name for clipping inside the loop due to poor design and
was, AIUI, understood by competent designers well before Mr Otala
produced his obfuscations.


Indeed. I was reading his article in Wireless World of 1975 or
thereabouts just the other day. His assertions about TIM just don't
stand up if the input conditions are defined properly. Audio input
signals have a defined bandwidth and defined level. If those are taken
into account in the power amplifier design, then TIM doesn't happen.

S.

On Wed, 07 Feb 2007 19:43:55 +0000, Serge Auckland
wrote:

Bill Taylor wrote:
On Wed, 7 Feb 2007 17:20:28 +0200, "Iain Churches"
wrote:

As an ex-patriot, I am probably often far more patriotic than
someone actually living in the UK. (Maybe distance lends
enchantment to the view:-)

The situation here in Scandinavia is much more healthy, it seems
to me.

In Sweden, everyone who knows anything at all about audio
can tell you about Per Johansson and the Swedish group of
researchers and experts from the renowned German Fraunhofer
Institute, who invented MP3.

Any Finn, who knows anything about audio is justly proud of
the achievements of Matti Otala, the man who first realised the
significance of intermodulation distortion in audio amps in 1973


ITYM transient intermodulation distorion; plain old IM had been known
about for decades.

His achievement was only significant in terms of publicity. TIM was
just another name for clipping inside the loop due to poor design and
was, AIUI, understood by competent designers well before Mr Otala
produced his obfuscations.


Indeed. I was reading his article in Wireless World of 1975 or
thereabouts just the other day. His assertions about TIM just don't
stand up if the input conditions are defined properly. Audio input
signals have a defined bandwidth and defined level. If those are taken
into account in the power amplifier design, then TIM doesn't happen.

S.

It is all about slew rate limiting - that is the mechanism that gives
rise to transient intermodulation distortion. You do, as you say, have
to make some assumptions about maximum levels and maximum frequencies.
With a digital source you can do that with a high degree of
confidence, but with an analogue one, there is always the opportunity
for stuff to be outside your assumed limits.

Of course slew rate limiting will only be a potential issue in an amp
containing a dominant pole cap which must be charged by the current in
the input stage. So poorer designs - no, or too small a dominant pole
cap - which might exhibit HF instability are less likely to suffer
TID.

d




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

In article , Don Pearce
wrote:


It is all about slew rate limiting - that is the mechanism that gives
rise to transient intermodulation distortion. You do, as you say, have
to make some assumptions about maximum levels and maximum frequencies.
With a digital source you can do that with a high degree of confidence,
but with an analogue one, there is always the opportunity for stuff to
be outside your assumed limits.

In practice, simply putting a passive LPF before the amp input resolves
that problem as it defines the maximum possible slew rate for a signal
whose amplitude would not also clip the amp. This is a trivially easy
'solution' that designers did almost without debate long prior to Otala's
publications and talks.

Although his ideas made a 'splash' in places like audio mags, my impression
what the most experienced designers thought he was making a mountain out of
a molehill and getting publicity for sticking a new label on a long-known
behaviour.

Out of curiosity I checked my texts by JLH and Self. JLH gives one brief
para to Otala. Self essentially dismisses him with a comment referring to
one of his papers.

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 Thu, 08 Feb 2007 09:27:23 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:


It is all about slew rate limiting - that is the mechanism that gives
rise to transient intermodulation distortion. You do, as you say, have
to make some assumptions about maximum levels and maximum frequencies.
With a digital source you can do that with a high degree of confidence,
but with an analogue one, there is always the opportunity for stuff to
be outside your assumed limits.

In practice, simply putting a passive LPF before the amp input resolves
that problem as it defines the maximum possible slew rate for a signal
whose amplitude would not also clip the amp. This is a trivially easy
'solution' that designers did almost without debate long prior to Otala's
publications and talks.

LPFs are good, but not much loved by manufacturers who play the
numbers game in their sales literature.

Although his ideas made a 'splash' in places like audio mags, my impression
what the most experienced designers thought he was making a mountain out of
a molehill and getting publicity for sticking a new label on a long-known
behaviour.

Out of curiosity I checked my texts by JLH and Self. JLH gives one brief
para to Otala. Self essentially dismisses him with a comment referring to
one of his papers.

I suspect Otala was doing no more than voicing facts that everybody
already knew.

d

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

In article , Don Pearce
wrote:
On Thu, 08 Feb 2007 09:27:23 +0000 (GMT), Jim Lesurf
wrote:



In practice, simply putting a passive LPF before the amp input resolves
that problem as it defines the maximum possible slew rate for a signal
whose amplitude would not also clip the amp. This is a trivially easy
'solution' that designers did almost without debate long prior to
Otala's publications and talks.

LPFs are good, but not much loved by manufacturers who play the numbers
game in their sales literature.

That may well be so. However if the amplifier is good enough it is quite
possible to use a filter whose passband extends to high frequencies. The
problem of omitting any such passive i/p filter is that you expose the amp
to 'RF' injection by that route, and risk problems no matter how good the
design in other respects.



Out of curiosity I checked my texts by JLH and Self. JLH gives one
brief para to Otala. Self essentially dismisses him with a comment
referring to one of his papers.

I suspect Otala was doing no more than voicing facts that everybody
already knew.

That is certainly my recollection.

IIRC the 'TID affair' appeared a couple of years before I started working
as a designer, so I mainly experienced it via consumer mags when he made
the claims, and then becoming personally involved a couple of years later.
However it was rapidly clear that he'd essentially just re-named something
which people already knew about and knew how to deal with if they were
capable engineers. Hence when I became involved in the biz I swiftly found
out that the designers I chatted to did not think that much of his work.

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