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[email protected] thekmanrocks@gmail.com is offline
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Default 90degree phase shifts

I'm guessing you all probably know why I need to create one of the above - to trick a Pro Logic Surround decoder.

Problem is, I know what a 90 - and 180 - deg phase shift looks like on a pure sinewave, but how to I achieve 90 degrees phase shift on "real world" material - a clip of ducks quacking or a 1890s locomotive roaring by? There is no simple wave - ducks, trains, and of course music - are anything but simple!
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Default 90degree phase shifts

субота, 28. јул 2012. 01.45.20 UTC+2, је написао/ла:
I'm guessing you all probably know why I need to create one of the above - to trick a Pro Logic Surround decoder.



Problem is, I know what a 90 - and 180 - deg phase shift looks like on a pure sinewave, but how to I achieve 90 degrees phase shift on "real world" material - a clip of ducks quacking or a 1890s locomotive roaring by? There is no simple wave - ducks, trains, and of course music - are anything but simple!


Pass it through capacitor. Not exactly 90deg, and different at freqs, but ...., or just delay it a ms, or so. Phase shift is meaningless on one isolated signal. You have to have at least two to experience the effect. In digital plug ins, you can try passing it through some old EQ, or something.
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Scott Dorsey Scott Dorsey is offline
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Default 90degree phase shifts

wrote:
I'm guessing you all probably know why I need to create one of the above - =
to trick a Pro Logic Surround decoder.


Why not use a pro logic encoder, then?

Problem is, I know what a 90 - and 180 - deg phase shift looks like on a pu=
re sinewave, but how to I achieve 90 degrees phase shift on "real world" ma=
terial - a clip of ducks quacking or a 1890s locomotive roaring by? There =
is no simple wave - ducks, trains, and of course music - are anything but s=
imple!


All-pass networks are discussed extensively in the Audio Cyclopedia.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default 90degree phase shifts

On 07/27/2012 05:44 PM, Scott Dorsey wrote:

All-pass networks are discussed extensively in the Audio Cyclopedia.
--scott


You'll need a bunch like a graphic EQ has bands for a range where each
all-pass is effective.

--



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Default 90degree phase shifts

You'll need a bunch like a graphic EQ


Phase is purely time-related. You can create a phasey effect by combing the eq channels but it's not the desired result.


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Default 90degree phase shifts

"David Gravereaux" wrote nothing in message
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Do you think you could post using one of our Earth newsreaders?




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Default 90degree phase shifts

On 07/27/2012 07:00 PM, None wrote:
"David Gravereaux" wrote nothing in message
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Do you think you could post using one of our Earth newsreaders?


Looks fine from
https://groups.google.com/d/msg/rec....I/4Tlb479N8M4J

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Default 90degree phase shifts

On 07/27/2012 06:23 PM, wrote:
You'll need a bunch like a graphic EQ


Phase is purely time-related. You can create a phasey effect by combing the eq channels but it's not the desired result.



See section 16.7 @
http://www.ti.com/lit/ml/sloa088/sloa088.pdf

--



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Default 90degree phase shifts

None wrote:

"David Gravereaux" wrote nothing in message
...


Do you think you could post using one of our Earth newsreaders?


He cannot. And hence, via my own newsreader he might as well be miming.

I gave up on his attitude about this a long time ago.

--
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Default 90degree phase shifts

Les Cargill wrote:

I have no idea how you do it in analog or in real time. But a
Hilbert Transform will provide a very good 90 degree phase
shift.


It will. Unfortunately when you run it through a Dolby CP-50 which uses
an all-pass filter (which is NOT a very good 90 degree phase shift), it
doesn't sound so good. You need to use filters on the encoding side
which are more or less the opposite of the ones on the decoding side.

I think that there are real time and analog versions of them;
I only know how to do to in the not-real time way.

As to the surround decoder - turn that off and do it
stereo. People still know how to do that.


Go to film-tech.com. Download the Dolby CP-50 manual. Look at the
phase shift networks on the Cat 146/150 card. Build the same networks
in reverse for encoding.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default 90degree phase shifts

"David Gravereaux" didn't write in message
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That's not a newsreader. It's an abomination.

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Default 90degree phase shifts

Scott Dorsey wrote:

Les Cargill wrote:

I have no idea how you do it in analog or in real time. But a
Hilbert Transform will provide a very good 90 degree phase
shift.


It will. Unfortunately when you run it through a Dolby CP-50 which uses
an all-pass filter (which is NOT a very good 90 degree phase shift), it
doesn't sound so good. You need to use filters on the encoding side
which are more or less the opposite of the ones on the decoding side.

I think that there are real time and analog versions of them;
I only know how to do to in the not-real time way.

As to the surround decoder - turn that off and do it
stereo. People still know how to do that.


Go to film-tech.com. Download the Dolby CP-50 manual. Look at the
phase shift networks on the Cat 146/150 card. Build the same networks
in reverse for encoding.


Sounds tricky.

--
shut up and play your guitar * http://hankalrich.com/
http://www.youtube.com/walkinaymusic
http://www.sonicbids.com/HankandShaidri
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Default 90degree phase shifts

Hank
"- show quoted text -
I'm wondering why one would want to trick a Dolby PLS decoder.
- show quoted text -
"

Because it's THERE.

THAT's why.
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Default 90degree phase shifts

Les Cargill wrote:

I have no idea how you do it in analog or in real time. But a
Hilbert Transform will provide a very good 90 degree phase
shift.


It will. *Unfortunately when you run it through a Dolby CP-50 which uses
an all-pass filter (which is NOT a very good 90 degree phase shift), it
do

Go to film-tech.com. *Download the Dolby CP-50 manual. *Look at the
phase shift networks on the Cat 146/150 card. * Build the same networks
in reverse for encoding.
- show quoted text -

Sorry Scott - Resource not found! Actually the filters are just below 100Hz and above 7kHz. I can do that in Audacity.


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Default 90degree phase shifts

hank alrich wrote:
Scott Dorsey wrote:

Les Cargill wrote:

I have no idea how you do it in analog or in real time. But a
Hilbert Transform will provide a very good 90 degree phase
shift.


It will. Unfortunately when you run it through a Dolby CP-50 which uses
an all-pass filter (which is NOT a very good 90 degree phase shift), it
doesn't sound so good. You need to use filters on the encoding side
which are more or less the opposite of the ones on the decoding side.

I think that there are real time and analog versions of them;
I only know how to do to in the not-real time way.

As to the surround decoder - turn that off and do it
stereo. People still know how to do that.


Go to film-tech.com. Download the Dolby CP-50 manual. Look at the
phase shift networks on the Cat 146/150 card. Build the same networks
in reverse for encoding.


Sounds tricky.


Y'know, if I'd practiced more, maybe I would have had to know all this.


That's what I keep telling myself anyway.

--
Les Cargill

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Default 90degree phase shifts

On 07/27/2012 06:23 PM, wrote:
You'll need a bunch like a graphic EQ


Phase is purely time-related. You can create a phasey effect by combing the eq channels but it's not the desired result.



Here's a rough assemblage in SPICE. Grab LTSpice from
http://www.linear.com/designtools/software/ to view it.

Obviously the summing overlaps improperly, but this is a rough idea
based on octave bands.

maintains a 90 shift between 300-6k or so.

--


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William Sommerwerck William Sommerwerck is offline
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Default 90degree phase shifts

You need two all-pass filters. One produces a phase shift of phi. The other
producers phi+90 or phi-90.

It is impossible to produce a fixed 90 degree phase shift over a wide
frequency range and have flat response at the same time. You have to create
the 90-degree shift as the difference between two filters' phase responses.

Trust me.


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Default 90degree phase shifts

wrote:

Hank
"- show quoted text -
I'm wondering why one would want to trick a Dolby PLS decoder.
- show quoted text -
"

Because it's THERE.

THAT's why.


It's a fine line between clever and stupid. I think you've crossed it.

--
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http://www.youtube.com/walkinaymusic
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Default 90degree phase shifts

hank alrich:
"It's a fine line between clever and stupid. I think you've crossed it. "
- show quoted text -

Keep your closed-minded remarks to yourself! At least others here have suggested ways to accomplish it or emulate it.


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Default 90degree phase shifts

Les Cargill wrote:
hank alrich wrote:
Scott Dorsey wrote:

Go to film-tech.com. Download the Dolby CP-50 manual. Look at the
phase shift networks on the Cat 146/150 card. Build the same networks
in reverse for encoding.


Sounds tricky.


Y'know, if I'd practiced more, maybe I would have had to know all this.


In the late eighties this sort of thing was all the rage. Everybody wanted to
make their own matrix surround tracks and nobody wanted to pay Dolby the
licensing fee for the encoder. There were lots of aftermarket fake Dolby
encoders sold, and a lot of homebrews. But now we have 5.1 and nobody much
bothers with any of that junk except as an afterthought for the occasional
film optical track.

So, it's sort of like the Phil Collins Drum Sound in that regard...
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default 90degree phase shifts

William Sommerwerck wrote:
You need two all-pass filters. One produces a phase shift of phi. The other
producers phi+90 or phi-90.

It is impossible to produce a fixed 90 degree phase shift over a wide
frequency range and have flat response at the same time. You have to create
the 90-degree shift as the difference between two filters' phase responses.


Yes. This is also discussed in Tremaine's Audio Cyclopedia which is the
first reference I recommended in this thread.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default 90degree phase shifts

wrote:

Go to film-tech.com. =A0Download the Dolby CP-50 manual. =A0Look at the=20
phase shift networks on the Cat 146/150 card. =A0 Build the same networks=
=20
in reverse for encoding.=20
- show quoted text -

Sorry Scott - Resource not found! Actually the filters are just below 100H=
z and above 7kHz. I can do that in Audacity.


Okay, class! Everybody pick up your keyboard and go to this url!
Yes, you have to start the browser and type it in on the top line.
Type http://www.film-tech.com all the way. Yes, you have to type
it all out. Now, wait for the page to load and click on WAREHOUSE
up at the top. Do you see WAREHOUSE? Now, click on MANUALS... does
everybody see MANUALS? That's where the manuals are stored...
--scott



--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default 90degree phase shifts

SD:
So, it's sort of like the Phil Collins Drum Sound in that regard...
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
___
And what issues do you have with Phil's drumming?
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Default 90degree phase shifts

On 7/27/2012 10:00 PM, None wrote:
"David Gravereaux" wrote nothing in
message ...


Do you think you could post using one of our Earth newsreaders?



Perhaps you need a real Earth newsreader. But he did put an
attachment in the posting which I didn't expect would come
through in rec.audio.pro.

What he said, less the attachment, was:

Here's a rough assemblage in SPICE. Grab LTSpice from
http://www.linear.com/designtools/software/ to view it.

Obviously the summing overlaps improperly, but this is a rough idea
based on octave bands.

maintains a 90 shift between 300-6k or so.



Or maybe you can find a surround encoder to pass your
recording through.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff


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Default 90degree phase shifts

"Mike Rivers" wrote in message
...
On 7/27/2012 10:00 PM, None wrote:
"David Gravereaux" wrote nothing in
message ...


Do you think you could post using one of our Earth newsreaders?

Perhaps you need a real Earth newsreader.


whooooosh!

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Default 90degree phase shifts

wrote in message
...
hank alrich:
"It's a fine line between clever and stupid. I think you've crossed it. "
- show quoted text -

Keep your closed-minded remarks to yourself! At least others here have
suggested ways to accomplish it or emulate it.


Q. Why would anyone want to reinvent the wheel?

A. Because it's fun, and you can learn something from it.

Sticking with the example, think for a minute about how you would go about
making a wheel if you were in the woods with nothing but an axe.

Sean


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Default 90degree phase shifts

William Sommerwerck wrote:
You need two all-pass filters. One produces a phase shift of phi. The other
producers phi+90 or phi-90.

It is impossible to produce a fixed 90 degree phase shift over a wide
frequency range and have flat response at the same time. You have to create
the 90-degree shift as the difference between two filters' phase responses.

Trust me.




So I just did an experiment which produced a fixed 90 degree phase
shift over the audio range.

I have some 'C' source which produces a Hilbert transform of an
audio file ( using libsndfile and FFTW plus some code of my own,
er code I pretty much swiped off the Internet .

When I run this twice*, I get perfect** cancellation

*Assume files A,B and C. B = Hilbert(A), C = Hilbert(B).

** to the limit of my ability to measure it. I can provide details on
request.

What am I missing?

--
Les Cargill




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Default 90degree phase shifts

On Sat, 28 Jul 2012 06:01:33 -0700, Scott Dorsey wrote
(in article ):

In the late eighties this sort of thing was all the rage. Everybody wanted

to
make their own matrix surround tracks and nobody wanted to pay Dolby the
licensing fee for the encoder. There were lots of aftermarket fake Dolby
encoders sold, and a lot of homebrews. But now we have 5.1 and nobody much
bothers with any of that junk except as an afterthought for the occasional
film optical track.
------------------------------snip------------------------------


Yes, this brings back memories of the 1980s with Ultra-Stereo, which I
believe was Jack Cashin's attempt to get around Dolby's patents and creating
a compatible (and much cheaper) matrixed surround system with a similar
noise-reduction encoding. I believe engineer John Mosely was also a
consultant for the company; Mosely had previously worked on Quintaphonic
sound in the mid-1970s. Interestingly, Dolby could not patent the surround
encoding itself, but did patent the noise reduction encoding (either Type A
or Type B, depending on the release format), which Ultra Stereo had to mimic
for their release prints. I used Ultra Stereo a few times in mastering, and
it actually worked OK.

To the o.p.: lots of books have the information necessary in order to
simulate a matrix surround mix. Dolby's own white paper is he

http://www.dolby.com/uploadedFiles/zz-
_Shared_Assets/English_PDFs/Professional/214_Mixing%20with%20Dolby%20Pro%20Log
ic%20II%20Technology.pdf

Tom Holman's book SURROUND SOUND: UP AND RUNNING also covers this in detail:

http://www.amazon.com/Surround-Sound-Second-Up-
running/dp/0240808290/ref=sr_1_2?s=books&ie=UTF8&qid=1343514433&sr=1-2

But in general, I agree with Scott -- I don't think matrix surround has any
point today, in the face of so many ways of discrete surround mixing and
digital release formats. Many DVD and Blu-ray releases are "upmixed" or
"unwrapped" in advance to take old 2-channel mixes and convert them to 5.1.
Done skillfully and with care, these can actually sound much better than any
of the old Dolby Matrix releases.

http://www.sersc.org/journals/IJSIP/vol2_no4/7.pdf

--MFW

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Default 90degree phase shifts

субота, 28. јул 2012. 21.57.27 UTC+2, Les Cargill је написао/ла:
William Sommerwerck wrote:

You need two all-pass filters. One produces a phase shift of phi. The other


producers phi+90 or phi-90.




It is impossible to produce a fixed 90 degree phase shift over a wide


frequency range and have flat response at the same time. You have to create


the 90-degree shift as the difference between two filters' phase responses.




Trust me.










So I just did an experiment which produced a fixed 90 degree phase

shift over the audio range.



I have some 'C' source which produces a Hilbert transform of an

audio file ( using libsndfile and FFTW plus some code of my own,

er code I pretty much swiped off the Internet .



When I run this twice*, I get perfect** cancellation



*Assume files A,B and C. B = Hilbert(A), C = Hilbert(B).



** to the limit of my ability to measure it. I can provide details on

request.



What am I missing?



--

Les Cargill


If you run make 4. one D=hilbert(C) does it, D, cancell out with B?


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Default 90degree phase shifts

Luxey wrote:
субота, 28. јул 2012. 21.57.27 UTC+2, Les Cargill је написао/ла:
William Sommerwerck wrote:

You need two all-pass filters. One produces a phase shift of phi. The other


producers phi+90 or phi-90.




It is impossible to produce a fixed 90 degree phase shift over a wide


frequency range and have flat response at the same time. You have to create


the 90-degree shift as the difference between two filters' phase responses.




Trust me.










So I just did an experiment which produced a fixed 90 degree phase

shift over the audio range.



I have some 'C' source which produces a Hilbert transform of an

audio file ( using libsndfile and FFTW plus some code of my own,

er code I pretty much swiped off the Internet .



When I run this twice*, I get perfect** cancellation



*Assume files A,B and C. B = Hilbert(A), C = Hilbert(B).



** to the limit of my ability to measure it. I can provide details on

request.



What am I missing?



--

Les Cargill


If you run make 4. one D=hilbert(C) does it, D, cancell out with B?



Yes, as you would suspect.

--
Les Cargill
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Default 90degree phase shifts

недеља, 29. јул 2012. 01.17.46 UTC+2, Les Cargill је написао/ла:
Luxey wrote:

субота, 28. јул 2012. 21.57.27 UTC+2, Les Cargill је написао/ла:


William Sommerwerck wrote:




You need two all-pass filters. One produces a phase shift of phi. The other




producers phi+90 or phi-90.








It is impossible to produce a fixed 90 degree phase shift over a wide




frequency range and have flat response at the same time. You have to create




the 90-degree shift as the difference between two filters' phase responses.








Trust me.




















So I just did an experiment which produced a fixed 90 degree phase




shift over the audio range.








I have some 'C' source which produces a Hilbert transform of an




audio file ( using libsndfile and FFTW plus some code of my own,




er code I pretty much swiped off the Internet .








When I run this twice*, I get perfect** cancellation








*Assume files A,B and C. B = Hilbert(A), C = Hilbert(B).








** to the limit of my ability to measure it. I can provide details on




request.








What am I missing?








--




Les Cargill




If you run make 4. one D=hilbert(C) does it, D, cancell out with B?








Yes, as you would suspect.



--

Les Cargill


I think it should not be so. B should be 90deg shift, while D should be 270deg shift. They should not cancel out, if complex signal.
If sine wave, it shoud cancel except for the first 1/4 of the first cycle and the last 1/4 of the last cycle. That's what I think. Very often I'm wrong.
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Default 90degree phase shifts

To clarify my thinking, seams if you apply function twice it does nos shift signal in phase for 180deg, but rather reverses it.
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Default 90degree phase shifts

Luxey wrote:
To clarify my thinking, seams if you apply function twice it does nos shift signal in phase for 180deg, but rather reverses it.


When the Hilbert transform is applied twice in succession to a function
u, the result is negative u:

H(H(u))(t) = -u(t),

provided the integrals defining both iterations converge in a suitable
sense. In particular, the inverse transform is H.

http://en.wikipedia.org/wiki/Hilbert_transform

--
Les Cargill

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Default 90degree phase shifts

Les Cargill wrote:
William Sommerwerck wrote:
You need two all-pass filters. One produces a phase shift of phi. The other
producers phi+90 or phi-90.

It is impossible to produce a fixed 90 degree phase shift over a wide
frequency range and have flat response at the same time. You have to create
the 90-degree shift as the difference between two filters' phase responses.

Trust me.

I have some 'C' source which produces a Hilbert transform of an
audio file ( using libsndfile and FFTW plus some code of my own,
er code I pretty much swiped off the Internet .

When I run this twice*, I get perfect** cancellation

What am I missing?


You can't do a Hilbert transform directly in the analogue domain. You can
only use some functions that approximate it, made with Ls and Cs.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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