[Les Cargill[_4_]]

I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

*does a 90 degree phase shift on the original signal - the algorithm
is painfully poorly exposed on the Wikipedia page - took me three tries
to find it.

This seems to work remarkably well. I know it's not really
stereo, but it's the best fake I've been able to find so far. One
should be able to use a fairly simple kernel with a convolver to
produce this.

Thoughts?

--
Les Cargill

[Don Pearce[_3_]]

On Thu, 22 Sep 2011 14:27:25 -0500, Les Cargill
wrote:


I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

*does a 90 degree phase shift on the original signal - the algorithm
is painfully poorly exposed on the Wikipedia page - took me three tries
to find it.

This seems to work remarkably well. I know it's not really
stereo, but it's the best fake I've been able to find so far. One
should be able to use a fairly simple kernel with a convolver to
produce this.

Thoughts?

I think I'd like to hear it. Can you post a sample?

d

[Les Cargill[_4_]]

Don Pearce wrote:
On Thu, 22 Sep 2011 14:27:25 -0500, Les Cargill
wrote:


I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

*does a 90 degree phase shift on the original signal - the algorithm
is painfully poorly exposed on the Wikipedia page - took me three tries
to find it.

This seems to work remarkably well. I know it's not really
stereo, but it's the best fake I've been able to find so far. One
should be able to use a fairly simple kernel with a convolver to
produce this.

Thoughts?

I think I'd like to hear it. Can you post a sample?

d

I don't have anything publishable saved. Lemme see.

--
Les Cargill

[Scott Dorsey]

Poster wrote:
"Les Cargill" wrote in message
...

I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

Would it be mono compatible?

If you sum the two, you get comb filtering.

To make it mono compatible, you mix a sum and difference of the original
signal and the all-passed signal, pan them right and left. This means
when you sum it to mono, you get the original signal.

This is how the classic Orban stereo simulator works.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ty Ford]

On Fri, 23 Sep 2011 09:32:49 -0400, Scott Dorsey wrote
(in article ):

Poster wrote:
"Les Cargill" wrote in message
...

I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

Would it be mono compatible?

If you sum the two, you get comb filtering.

To make it mono compatible, you mix a sum and difference of the original
signal and the all-passed signal, pan them right and left. This means
when you sum it to mono, you get the original signal.

This is how the classic Orban stereo simulator works.
--scott


I love rec.audio.pro!

Regards,

Ty Ford


--Audio Equipment Reviews Audio Production Services
Acting and Voiceover Demos http://www.tyford.com
Guitar player?:http://www.youtube.com/watch?v=yWaPRHMGhGA

[Les Cargill[_4_]]

Poster wrote:
"Les wrote in message
...

I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

Would it be mono compatible?





Good question. I'd think so.

--
Les Cargill

[MarkK]

I recently wrote a Hilbert transformer* for .wav files, as an
exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

Would it be mono compatible?

If you sum the two, you get comb filtering.



1) An X/Y pair is not acoustic quadrature. The mics are coincident so
there is little or no phase information, it's all intensity information.

2) A HT is a 90 deg shift at all frequencies. It's not very intuitive. I
don't think you will get comb filtering summing to mono because it is 90 deg
at all frequencies. Comb filtering is caused by a fixed time delay that
causes a variable phase shift that varies through 0 and 180 causing
additions and cancellations. An HT is 90 deg at all frequencies.

3) All that being said, it probably does spread a mono source pretty well.

Mark

[William Sommerwerck]

2) A HT is a 90 deg shift at all frequencies. It's not very intuitive. I
don't think you will get comb filtering summing to mono because it is 90
deg
at all frequencies. Comb filtering is caused by a fixed time delay that
causes a variable phase shift that varies through 0 and 180 causing
additions and cancellations. An HT is 90 deg at all frequencies.

The only practical way to achieve it is with a pair of all-pass filters, of
phi and phi+90 (or phi-90). These were uised in most matrix-quad systems.


3) All that being said, it probably does spread a mono source pretty well.

One way to "spread" a mono source -- without altering it in any way! -- is
to synthesize hall reverb and play the reverb through additional speakers.
You'd probably be amazed at the improvement.

[Les Cargill[_4_]]

MarkK wrote:

I recently wrote a Hilbert transformer* for .wav files, as an
exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

Would it be mono compatible?

If you sum the two, you get comb filtering.



1) An X/Y pair is not acoustic quadrature. The mics are coincident so
there is little or no phase information, it's all intensity information.


I didn't mean *literally* quadrature. I put that in
scare quotes for a reason Both involve the
phrase "90 degrees". I'm not being severely rigorous here,
just musing. it's more an art concept than a science one.

So the idea is to use the HT to "simulate" the second mic
of an X/Y pair. And yes, it's a naive initial idea, not something
derived from the ... solution of differential equations

but apparently, Bob Orban did something similar, so it's
not a completely stupid idea

And they say "it's intensity", but each card element is a "phase"
based cancel-ifier, so ... it might be interesting to see the
convolution between the two mics in an X/Y, but I don't know
where to put the impulse...

2) A HT is a 90 deg shift at all frequencies. It's not very intuitive. I
don't think you will get comb filtering summing to mono because it is 90 deg
at all frequencies. Comb filtering is caused by a fixed time delay that
causes a variable phase shift that varies through 0 and 180 causing
additions and cancellations. An HT is 90 deg at all frequencies.

3) All that being said, it probably does spread a mono source pretty well.

Mark




--
Les Cargill

[Les Cargill[_4_]]

William Sommerwerck wrote:
2) A HT is a 90 deg shift at all frequencies. It's not very intuitive. I
don't think you will get comb filtering summing to mono because it is 90
deg
at all frequencies. Comb filtering is caused by a fixed time delay that
causes a variable phase shift that varies through 0 and 180 causing
additions and cancellations. An HT is 90 deg at all frequencies.

The only practical way to achieve it is with a pair of all-pass filters, of
phi and phi+90 (or phi-90). These were uised in most matrix-quad systems.


3) All that being said, it probably does spread a mono source pretty well.

One way to "spread" a mono source -- without altering it in any way! -- is
to synthesize hall reverb and play the reverb through additional speakers.
You'd probably be amazed at the improvement.




Absolutely. Indeed, this, then a reverb sounds pretty lifelike.

--
Les Cargill

[Les Cargill[_4_]]

Don Pearce wrote:
On Thu, 22 Sep 2011 14:27:25 -0500, Les Cargill
wrote:


I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

*does a 90 degree phase shift on the original signal - the algorithm
is painfully poorly exposed on the Wikipedia page - took me three tries
to find it.

This seems to work remarkably well. I know it's not really
stereo, but it's the best fake I've been able to find so far. One
should be able to use a fairly simple kernel with a convolver to
produce this.

Thoughts?

I think I'd like to hear it. Can you post a sample?

d


Try this:

http://soundcloud.com/les-cargill/phase

It's:

- Original panned center.
- HT left
- Polarity-inverted-HT right.

The first half is just the "fake stereo"; the second half is fake
stereo plus some room reverb.

I dunno. Sounds kinda weird by itself now, kinda "twist your
head off"-ey.

--
Les Cargill

[Don Pearce[_3_]]

On Sat, 24 Sep 2011 15:15:12 -0500, Les Cargill
wrote:

Don Pearce wrote:
On Thu, 22 Sep 2011 14:27:25 -0500, Les Cargill
wrote:


I recently wrote a Hilbert transformer* for .wav files, as an exercise.
So I got curious - since X/Y is basically "acoustic quadrature", how
would it sound to spread a mono source left, with the Hilbertized
signal panned right?

*does a 90 degree phase shift on the original signal - the algorithm
is painfully poorly exposed on the Wikipedia page - took me three tries
to find it.

This seems to work remarkably well. I know it's not really
stereo, but it's the best fake I've been able to find so far. One
should be able to use a fairly simple kernel with a convolver to
produce this.

Thoughts?

I think I'd like to hear it. Can you post a sample?

d


Try this:

http://soundcloud.com/les-cargill/phase

It's:

- Original panned center.
- HT left
- Polarity-inverted-HT right.

The first half is just the "fake stereo"; the second half is fake
stereo plus some room reverb.

I dunno. Sounds kinda weird by itself now, kinda "twist your
head off"-ey.

That's really interesting. Through speakers it sounds as you describe.
But through headphones, the first half just sounds like mono, while in
the second I can hear the fake reverb.

d

[Scott Dorsey]

Les Cargill wrote:
Scott Dorsey wrote:
To make it mono compatible, you mix a sum and difference of the original
signal and the all-passed signal, pan them right and left. This means
when you sum it to mono, you get the original signal.

This is how the classic Orban stereo simulator works.

Aha! There we go. I knew it couldn't be new.

Well, in one sense it's new in that the transform gives you a much cleaner
and more accurate phase shift than an analogue all-pass network gives you.
So yes, the comb filtering issues are eliminated which is something I hadn't
thought about.

Phase shift networks for generating single sideband audio have been around
since the early fifties, but doing it in the digital domain to generate
single sideband audio that actually sounds decent and has low group delay
is a new thing.

Likewise SQ and QS matrix quad decoding, which the Hilbert transform can
do far more cleanly than the all-pass networks.

It is interesting, though, to note that almost all audio design techniques
we use today can be found in 1930s copies of the Bell System Technical
Journal in some form or another. It's amazing how little there is new under
the sun.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."