Reply by robert bristow-johnson●November 20, 20102010-11-20
On Nov 20, 8:54�am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
> On Fri, 19 Nov 2010 11:00:06 -0800 (PST), robert bristow-johnson
>
> <r...@audioimagination.com> wrote:
>
> � �[Snipped by Lyons]
>
>
>
>
>
> >...
> >> � I did my best to avoid using the phrase
> >> "Nyquist frequency."
>
> >i know you did in the first two editions. �as i said, it might have
> >been smart to avoid a tiff regarding semantics.
>
> >but i believe we have language and words for a reason (that is, of
> >efficiency of communication). �i don't say "my 4-wheeled personal
> >vehicle" every time i mean "my car". �nor do i say "the identity that
> >translates the natural exponential of an imaginary argument to
> >sinusoidal functions" when i mean "Euler's formula". �when someone
> >else takes issue with these semantics and says "'car' could mean
> >something that runs on rails" or "that's really Roger Cotes' formula",
> >i just want to tell them that the names have settled meaning and it's
> >efficient if we leave them as settled.
>
> >> �When I was referring
> >> to half the sample rate I attempted by be
> >> as clear as possible by using the term "Fs/2."
>
> >grrr. �i just wanted you (as another author) to make a stand on the
> >semantic issue (and take the *correct* stand).
>
> >L8r,
>
> >r b-j
>
> Hi Robert,
> � �you wrote: �"... the names have settled meaning(s) ..."
> but you admitted that sometimes two people have
> two different meanings for the same word.
> I don't believe that the names are "settled."
>
> The problem as I see it is: �I've seen the phrases,
>
> � �"Nyquist frequency"
??? hadn't really heard of Nyquist bandwidth myself.
> used in the literature. �And when I read one of
> those phrases (terminology) in a DSP paper, I cannot
> be sure what the author means!! �So then I have to
> go back to the beginning of paper and start searching
> to see if the author defined what he means by the
> phrase "Nyquist frequency", for example.
which is why we all need to be consistent with the semantics. one way
to do that is to consistently use the "correct" semantic.
>
> Think of this, suppose �in Chapter 1 I state that
> "In this text, "Nyquist frequency" means Fs/2."
> Then some guy pulls my book off a colleague's bookshelf
> and starts reading Chapter 8. �And in that chapter
> he encounters the phrase "Nyquist frequency." �
> He cannot be *SURE* what that phrase means, so he has
> to start rifling through earlier chapters hoping to
> find my "In this text, "Nyquist frequency" means
> Fs/2" sentence somewhere. �Why should I put the
> reader through that kind of torment?
>
> So what did I do? �In Chapter 8 when I meant Fs/2
> I came right out and wrote "Fs/2" so there's
> uncertainty.
maybe restate it the definition at the first use in Ch 8.
r b-j
Reply by Rick Lyons●November 20, 20102010-11-20
On Fri, 19 Nov 2010 11:00:06 -0800 (PST), robert bristow-johnson
<rbj@audioimagination.com> wrote:
[Snipped by Lyons]
>>
>...
>> � I did my best to avoid using the phrase
>> "Nyquist frequency."
>
>i know you did in the first two editions. as i said, it might have
>been smart to avoid a tiff regarding semantics.
>
>but i believe we have language and words for a reason (that is, of
>efficiency of communication). i don't say "my 4-wheeled personal
>vehicle" every time i mean "my car". nor do i say "the identity that
>translates the natural exponential of an imaginary argument to
>sinusoidal functions" when i mean "Euler's formula". when someone
>else takes issue with these semantics and says "'car' could mean
>something that runs on rails" or "that's really Roger Cotes' formula",
>i just want to tell them that the names have settled meaning and it's
>efficient if we leave them as settled.
>
>> �When I was referring
>> to half the sample rate I attempted by be
>> as clear as possible by using the term "Fs/2."
>
>grrr. i just wanted you (as another author) to make a stand on the
>semantic issue (and take the *correct* stand).
>
>L8r,
>
>r b-j
Hi Robert,
you wrote: "... the names have settled meaning(s) ..."
but you admitted that sometimes two people have
two different meanings for the same word.
I don't believe that the names are "settled."
The problem as I see it is: I've seen the phrases,
"Nyquist frequency"
"half Nyquist frequency"
"Nyquist rate"
"Nyquist bandwidth"
used in the literature. And when I read one of
those phrases (terminology) in a DSP paper, I cannot
be sure what the author means!! So then I have to
go back to the beginning of paper and start searching
to see if the author defined what he means by the
phrase "Nyquist frequency", for example.
Think of this, suppose in Chapter 1 I state that
"In this text, "Nyquist frequency" means Fs/2."
Then some guy pulls my book off a colleague's bookshelf
and starts reading Chapter 8. And in that chapter
he encounters the phrase "Nyquist frequency."
He cannot be *SURE* what that phrase means, so he has
to start rifling through earlier chapters hoping to
find my "In this text, "Nyquist frequency" means
Fs/2" sentence somewhere. Why should I put the
reader through that kind of torment?
So what did I do? In Chapter 8 when I meant Fs/2
I came right out and wrote "Fs/2" so there's
uncertainty.
See Ya',
[-Rick-]
Reply by Rick Lyons●November 20, 20102010-11-20
On Wed, 17 Nov 2010 05:16:14 -0800 (PST), Rune Allnor
<allnor@tele.ntnu.no> wrote:
>On Nov 17, 12:20�pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
>
>> I mention that because the International Version's
>> homework problems are different from the American
>> Version's homework problems.
>
>Interesting! In what ways?
>
>Rune
Hi Rune,
here are examples of a homework problem
in the various versions:
Asian Edition:
A logger sells a truckload of lumber for $100.
His cost of production is 4/5 of that price.
What is his profit?
Norwegian Edition:
A logger sells a truckload of lumber for $100.
His cost of production is $80. Did he make a profit?
American Edition:
A logger cuts down a beautiful forest because he
cares nothing for the habitat of animals or the
preservation of our woodlands. He does this so
he can make a profit of $20.
What do you think of this way of making a living?
Topic for class discussion: How did the birds and
squirrels feel as the logger cut down their homes?
(There are no wrong answers.)
:-) :-) :-)
OK OK, I'll stop clowning around. The International
Version's homework problems are "intellectually" the
same as the American Version's homework problems.
There's no difference in the "problem difficulty"
between the two versions.
It's the Publisher's policy to have two sets (two
versions) of homework problems---so that if the American
version is used as a classroom text in America, then
an International version of the book will not be
useful in doing the homework for the American class.
See Ya',
[-Rick-]
Reply by rickman●November 19, 20102010-11-19
On Nov 19, 2:00�pm, robert bristow-johnson <r...@audioimagination.com>
wrote:
> On Nov 19, 10:17�am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
>
>
>
> > On Thu, 18 Nov 2010 09:34:49 -0800 (PST), robert bristow-johnson
>
> > <r...@audioimagination.com> wrote:
> > >On Nov 17, 6:13 am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
> > >> On Tue, 16 Nov 2010 06:20:44 GMT, Al Clark <acl...@danvillesignal.com>
> > >> wrote:
>
> > >> >I just noticed that Rick Lyon's 3rd edition of Understanding Digital Signal
> > >> >Processing is out, so I guess I will have to get a copy to place next to the
> > >> >1st & 2nd editions on my bookshelf.
>
> > >> >I've always considered Rick's book the definitive DSP primer.
>
> > >> >There are two kinds of engineers, those who can't write and those who can
> > >> >barely write. I strive for the latter. Rick is the clear exception to the
> > >> >rule.
>
> > >> Yep, the 3rd Edition is *FINALLY* finished.
> > >> Whew!
>
> > >> Thanks for the kind words Al.
>
> > >hay Rick, not an unkind word, just a question: �does your 3rd edition
> > >take a position of the meaning of "Nyquist frequency"? �3 different
> > >definitions i have seen:
>
> > > Nyquist frequency = � a) �Fs/2
> > > � � � � � � � � � � � b) �B (bandlimit of signal to be sampled)
> > > � � � � � � � � � � � c) �Fs (rarely)
> > > � � � � � � � � � � � d) �2B (usually called the "Nyquist rate")
>
> > >several years ago, when this definition discussion came up, i was
> > >appalled to find that O&S themselves had the wrong definition (at
> > >least in my 1989 edition). �and surprized to see Rick was sorta
> > >agnostic about it (maybe that was smart).
>
> ...
> > � I did my best to avoid using the phrase
> > "Nyquist frequency."
>
> i know you did in the first two editions. �as i said, it might have
> been smart to avoid a tiff regarding semantics.
>
> but i believe we have language and words for a reason (that is, of
> efficiency of communication). �i don't say "my 4-wheeled personal
> vehicle" every time i mean "my car". �nor do i say "the identity that
> translates the natural exponential of an imaginary argument to
> sinusoidal functions" when i mean "Euler's formula". �when someone
> else takes issue with these semantics and says "'car' could mean
> something that runs on rails" or "that's really Roger Cotes' formula",
> i just want to tell them that the names have settled meaning and it's
> efficient if we leave them as settled.
>
> > �When I was referring
> > to half the sample rate I attempted by be
> > as clear as possible by using the term "Fs/2."
>
> grrr. �i just wanted you (as another author) to make a stand on the
> semantic issue (and take the *correct* stand).
Don't we all... don't we all...
Rick
Reply by Ala●November 19, 20102010-11-19
"richard i pelletier" <bitbucket@comcast.net> wrote in message
news:bitbucket-A3DD1E.16100117112010@news.supernews.com...
> In article
> <841d53dc-8023-4c01-bbf9-50aacf6a7606@j2g2000yqf.googlegroups.com>,
> davew <david.wooff@gmail.com> wrote:
>
>> I think JOS's book on the discrete
>> Fourier Transform is also a great book for the same reasons.
>
> I don't recognize "JOS".... can you tell me what author and book you are
> praising? I might buy it.
>
So cute
Reply by glen herrmannsfeldt●November 19, 20102010-11-19
> On Thu, 18 Nov 2010 19:52:57 -0800 (PST), rickman <gnuarm@gmail.com> wrote:
>>I'm not sure where you are getting that. It is correct if you are
>>using complex numbers, but if you are sampling a real signal there is
>>no imaginary part, so the only signal is real and no negative
>>frequencies.
> Incorrect. Sample any real signal and you get a negative spectrum
> between 0 and -Fs/2 that is the complex conjugate of the positive
> spectrum between 0 and +Fs/2. The bandwidth is Fs.
>>But a sample rate of Fs can't represent a real signal
>>with a wider bandwidth than Fs/2. Try it, you will see that all
>>frequencies outside of 0 to Fs/2 get aliased into that frequency
>>range.
> Given a real signal of one-sided bandwidth B (i.e., under the
> common definition that excludes negative frequencies, the bandwidth
> extends from DC to B), it can be unambiguously sampled at Fs > 2B.
> Amplitude-modulate that same signal by a carrier of frequency C.
> The resulting AM spectrum will extend from +C-B to +C+B (and also
> from -C+B to -C-B). Under the common definition it will have a
> bandwidth of 2B, yet it can still be unambiguously sampled by
> any Fs > 2B.
Yes, AM uses bandwidth inefficiently. If you use an SSB modulator,
or have two signals and use QAM, then you use bandwidth more
efficiently. You could also use FM, and waste even more bandwidth.
> Now set C = 0. The bandwidth hasn't changed, but the negative
> image now overlaps the positive image exactly. So why is the
> bandwidth now B instead of 2B?
> The problem is in the definition of bandwidth.
There has to be a 2 in there somewhere. Using the inefficient AM
as a source of the 2 doesn't seem quite fair.
It is nice to try to hide the 2, but you can't really get
rid of it.
-- glen
Reply by glen herrmannsfeldt●November 19, 20102010-11-19
>> >> Everybody seems to forget that a signal extending from DC to Fs/2 also
>> >> extends from DC to -Fs/2, so the bandwidth is actually Fs. �So Fs can
>> >> unambiguously represent a bandwidth incrementally less than Fs.
>> > That is only a way of interpreting the math... there is a reason why
>> > they call them "real" and "imaginary" numbers. �Negative frequency???
>> > Think about what that means in the physical world... �:^)
(then I wrote)
>> OK, but with a synchronous demodulator you can separate out
>> the I and Q, or sine and cosine parts, as the NTSC color
>> subcarrier demodulators do (did). �
>> If you don't like imaginary numbers, use the Hartley transform instead.
>> Then there are still sine and cosine, or even and odd, components,
>> but with real input only real output.
> That's not the point. The question is about what it takes to
> represent a signal. When you sample a signal (the only thing the
> Nyquist criterion relates to) you must sample at twice the band width
> to capture all information intact. Then you can play games with that
> data and reduce the "sample rate", although you just reformatting the
> data to use two components per sample with half the sample rate. In
> reality you have not really gotten around the Nyquist criterion.
I completely agree. The comment had to do with signals being real,
and that the imaginary component couldn't be sampled.
Yes, with the ones I described you need two real values at each
sample interval, and that is not a lot different than one real
value at twice the rate. It is comparable to real and imaginary
components at the lower rate.
(snip)
>> As NTSC puts two parts of the color subcarrier into
>> the bandwidth needed for one.
-- glen
Reply by robert bristow-johnson●November 19, 20102010-11-19
On Nov 19, 10:17�am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
> On Thu, 18 Nov 2010 09:34:49 -0800 (PST), robert bristow-johnson
>
>
>
> <r...@audioimagination.com> wrote:
> >On Nov 17, 6:13 am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
> >> On Tue, 16 Nov 2010 06:20:44 GMT, Al Clark <acl...@danvillesignal.com>
> >> wrote:
>
> >> >I just noticed that Rick Lyon's 3rd edition of Understanding Digital Signal
> >> >Processing is out, so I guess I will have to get a copy to place next to the
> >> >1st & 2nd editions on my bookshelf.
>
> >> >I've always considered Rick's book the definitive DSP primer.
>
> >> >There are two kinds of engineers, those who can't write and those who can
> >> >barely write. I strive for the latter. Rick is the clear exception to the
> >> >rule.
>
> >> Yep, the 3rd Edition is *FINALLY* finished.
> >> Whew!
>
> >> Thanks for the kind words Al.
>
> >hay Rick, not an unkind word, just a question: �does your 3rd edition
> >take a position of the meaning of "Nyquist frequency"? �3 different
> >definitions i have seen:
>
> > Nyquist frequency = � a) �Fs/2
> > � � � � � � � � � � � b) �B (bandlimit of signal to be sampled)
> > � � � � � � � � � � � c) �Fs (rarely)
> > � � � � � � � � � � � d) �2B (usually called the "Nyquist rate")
>
> >several years ago, when this definition discussion came up, i was
> >appalled to find that O&S themselves had the wrong definition (at
> >least in my 1989 edition). �and surprized to see Rick was sorta
> >agnostic about it (maybe that was smart).
>
...
> � I did my best to avoid using the phrase
> "Nyquist frequency."
i know you did in the first two editions. as i said, it might have
been smart to avoid a tiff regarding semantics.
but i believe we have language and words for a reason (that is, of
efficiency of communication). i don't say "my 4-wheeled personal
vehicle" every time i mean "my car". nor do i say "the identity that
translates the natural exponential of an imaginary argument to
sinusoidal functions" when i mean "Euler's formula". when someone
else takes issue with these semantics and says "'car' could mean
something that runs on rails" or "that's really Roger Cotes' formula",
i just want to tell them that the names have settled meaning and it's
efficient if we leave them as settled.
> �When I was referring
> to half the sample rate I attempted by be
> as clear as possible by using the term "Fs/2."
grrr. i just wanted you (as another author) to make a stand on the
semantic issue (and take the *correct* stand).
L8r,
r b-j
Reply by Greg Berchin●November 19, 20102010-11-19
On Fri, 19 Nov 2010 07:43:20 -0600, jim <"sjedgingN0Sp"@m@mwt,net> wrote:
>> > Wouldn't you name that the "Nyquist bandwidth"? The Nyquist frequency would be
>> > the maximum frequency that can be represented by a given sample rate, in other
>> > words Fs/2.
>>
>> No,
>
>What is it you are saying No to? If someone is talking about bandwidth
>why would they call it frequency?
I didn't trim enough of the quote. I was saying "no" to "the maximum frequency
that can be represented by a given sample rate, in other words Fs/2." The
maximum *bandwidth* that can be represented by Fs is incrementally less than Fs,
under conditions stated in some of my other posts.
Greg
Reply by Rick Lyons●November 19, 20102010-11-19
On Thu, 18 Nov 2010 09:34:49 -0800 (PST), robert bristow-johnson
<rbj@audioimagination.com> wrote:
>On Nov 17, 6:13�am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
>> On Tue, 16 Nov 2010 06:20:44 GMT, Al Clark <acl...@danvillesignal.com>
>> wrote:
>>
>> >I just noticed that Rick Lyon's 3rd edition of Understanding Digital Signal
>> >Processing is out, so I guess I will have to get a copy to place next to the
>> >1st & 2nd editions on my bookshelf.
>>
>> >I've always considered Rick's book the definitive DSP primer.
>>
>> >There are two kinds of engineers, those who can't write and those who can
>> >barely write. I strive for the latter. Rick is the clear exception to the
>> >rule.
>>
>> � Yep, the 3rd Edition is *FINALLY* finished.
>> Whew!
>>
>> Thanks for the kind words Al.
>
>hay Rick, not an unkind word, just a question: does your 3rd edition
>take a position of the meaning of "Nyquist frequency"? 3 different
>definitions i have seen:
>
>
> Nyquist frequency = a) Fs/2
> b) B (bandlimit of signal to be sampled)
> c) Fs (rarely)
> d) 2B (usually called the "Nyquist rate")
>
>
>several years ago, when this definition discussion came up, i was
>appalled to find that O&S themselves had the wrong definition (at
>least in my 1989 edition). and surprized to see Rick was sorta
>agnostic about it (maybe that was smart).
>
>r b-j
Hi Robert,
I did my best to avoid using the phrase
"Nyquist frequency." When I was referring
to half the sample rate I attempted by be
as clear as possible by using the term "Fs/2."
[-Rick-]