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James Price[_6_] James Price[_6_] is offline
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Default Why don't these signals null?

Let's say I record a DI guitar part into a looper, then re-amp that looped part and record the output twice to separate tracks in a DAW, time-align them and invert the phase on one. I know the tracks won't null, but I don't fully understand the why.
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John Williamson John Williamson is offline
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Default Why don't these signals null?

On 17/10/2019 06:51, James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that looped part and record the output twice to separate tracks in a DAW, time-align them and invert the phase on one. I know the tracks won't null, but I don't fully understand the why.

When you re-amp the part, that changes the waveform in both shape and
amplitude, so it will not null out. To null completely, the waveforms
and the amplitudes of the two tracks have to be identical.

--
Tciao for Now!

John.
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Default Why don't these signals null?

On Thursday, October 17, 2019 at 2:12:02 AM UTC-5, John Williamson wrote:
When you re-amp the part, that changes the waveform in both shape and
amplitude, so it will not null out. To null completely, the waveforms
and the amplitudes of the two tracks have to be identical.


I'm talking about re-amping the part using a looper in order to
eliminate any inconsistencies that would normally occur when playing the
part twice.
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John Williamson John Williamson is offline
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Default Why don't these signals null?

On 17/10/2019 19:01, James Price wrote:
I'm talking about re-amping the part using a looper in order to
eliminate any inconsistencies that would normally occur when playing the
part twice.

Are you recording the part, saving that as one track in the mix, then
re-amping that recording using a plugin and saving that as another track?

If so, then the re-amped version will not be identical to the original
recording due to the changes made by the plug in. There will be changes
in the frequency response as a minimum. What you will hear when you
invert the phase of one of the tracks is the difference added by the
re-amp plugin.

Or are you just copying the original recording to another track in the
mix? In which case they should null exactly unless the settings on the
two tracks differ.

--
Tciao for Now!

John.
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James Price[_6_] James Price[_6_] is offline
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Default Why don't these signals null?

On Thursday, October 17, 2019 at 1:21:07 PM UTC-5, John Williamson wrote:
On 17/10/2019 19:01, James Price wrote:
I'm talking about re-amping the part using a looper in order to
eliminate any inconsistencies that would normally occur when playing the
part twice.

Are you recording the part, saving that as one track in the mix, then
re-amping that recording using a plugin and saving that as another track?


I've done that, and also recorded a DI to a track in a DAW using a DI box
and routed the output from the interface to a miked cab, which is recorded
twice (separate passes) to two tracks into the DAW.


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Phil Allison[_4_] Phil Allison[_4_] is offline
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Default Why don't these signals null?

John Williamson wrote:

-----------------------

Or are you just copying the original recording to another track in the
mix? In which case they should null exactly unless the settings on the
two tracks differ.


** IMO you are wasting your time - the OP is an idiot.

Reminds me of an event years ago when a local small studio operator had a problem with his Yamaha REV 7 digital reverb.

On the phone he claimed it had stopped working in stereo - he could no longer pan pot sounds coming out in in a stereo mix.

Being an unfamiliar model to me, I agreed to take a quick look at it and soon realised the despite having L & R inputs and outputs, it was not a genuine stereo unit but rather it simulated stereo from a mono path at the output.

His claim that it used to work in true stereo was bogus, but nothing I said would convince him otherwise. He eventually picked up the unit and left in a huff to find a better tech.

His business card said "Enterprise Studios" with a pen drawing of the famous space ship.

So I dubbed the guy "Captain Jerk".


..... Phil




















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Default Why don't these signals null?

On 18/10/2019 8:55 am, James Price wrote:
On Thursday, October 17, 2019 at 1:21:07 PM UTC-5, John Williamson wrote:
On 17/10/2019 19:01, James Price wrote:
I'm talking about re-amping the part using a looper in order to
eliminate any inconsistencies that would normally occur when playing the
part twice.

Are you recording the part, saving that as one track in the mix, then
re-amping that recording using a plugin and saving that as another track?


I've done that, and also recorded a DI to a track in a DAW using a DI box
and routed the output from the interface to a miked cab, which is recorded
twice (separate passes) to two tracks into the DAW.


.... and you're wondering why they don't completely null ?!!!

geoff
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Default Why don't these signals null?

On Thursday, October 17, 2019 at 5:52:58 PM UTC-5, geoff wrote:
... and you're wondering why they don't completely null ?!!!



The caveat is that they will null completely with clean tones.
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Tobiah Tobiah is offline
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Default Why don't these signals null?

On 10/16/19 10:51 PM, James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that
looped part and record the output twice to separate tracks in a DAW,
time-align them and invert the phase on one. I know the tracks won't
null, but I don't fully understand the why.


When you run the signal through an amp, through the air, into a microphone
you open yourself up to some variables that may change between passes. Were
you in the room during the recordings? Did you move at all, or breath with
a different pattern the second time? Was the ambient noise exactly the same
both times? The acoustic space that you sent the signals through will never
be the same during both passes. Even if you recorded the straight and inverted
tracks at the same time, you'd use two different mics that would collect altogether
different signals because of their mismatch, and necessarily different positions.

Also, you say you time aligned the two tracks, but did you get that sample perfect?
what about clock drift that may have been different between takes?

What was the result anyway, if not null? Was it pretty quiet anyway?


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Default Why don't these signals null?

On Friday, October 18, 2019 at 10:47:52 AM UTC-5, Tobiah wrote:
On 10/16/19 10:51 PM, James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that
looped part and record the output twice to separate tracks in a DAW,
time-align them and invert the phase on one. I know the tracks won't
null, but I don't fully understand the why.


When you run the signal through an amp, through the air, into a microphone
you open yourself up to some variables that may change between passes. Were
you in the room during the recordings? Did you move at all, or breath with
a different pattern the second time? Was the ambient noise exactly the same
both times? The acoustic space that you sent the signals through will never
be the same during both passes. Even if you recorded the straight and inverted
tracks at the same time, you'd use two different mics that would collect altogether
different signals because of their mismatch, and necessarily different positions.


These were short (approx. 10 seconds), close-miked recordings, recorded
in two passes, back-to-back using the same mic, through the same cab and fed
a DI guitar via a sampled loop. The recordings were time-aligned perfectly at
the sample level.


What was the result anyway, if not null? Was it pretty quiet anyway?


The residual noise fluctuated somewhere between -30 to -50 dB.


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John Williamson John Williamson is offline
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Default Why don't these signals null?

On 18/10/2019 17:24, James Price wrote:

These were short (approx. 10 seconds), close-miked recordings, recorded
in two passes, back-to-back using the same mic, through the same cab and fed
a DI guitar via a sampled loop. The recordings were time-aligned perfectly at
the sample level.


No two recordings of any instrument (Whether digital or analogue) played
by a human will ever null completely. Apart from environmental factors
such as the air temperature, the player's will differ timing between the
two recordings.

Getting them as close as you did is actually damn consistent playing.


--
Tciao for Now!

John.
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Default Why don't these signals null?

On 10/18/2019 1:04 PM, John Williamson wrote:
On 18/10/2019 17:24, James Price wrote:

These were short (approx. 10 seconds), close-miked recordings, recorded
in two passes, back-to-back using the same mic, through the same cab
and fed
a DI guitar via a sampled loop. The recordings were time-aligned
perfectly at
the sample level.


No two recordings of any instrument (Whether digital or analogue) played
by a human will ever null completely. Apart from environmental factors
such as the air temperature, the player's will differ timing between the
two recordings.

Getting them as close as you did is actually damn consistent playing.


His original post was difficult to understand, but if you look at it
again, he performs once, then copies the track through the air twice.
The result he got is to be expected. The inverted track mostly nulled
the other, but the differences caused by amp distortion and air medium
inconsistencies and even his position in the room, lingered in the
difference.



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James Price[_6_] James Price[_6_] is offline
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Default Why don't these signals null?

On Friday, October 18, 2019 at 3:04:40 PM UTC-5, John Williamson wrote:
On 18/10/2019 17:24, James Price wrote:

These were short (approx. 10 seconds), close-miked recordings, recorded
in two passes, back-to-back using the same mic, through the same cab and fed
a DI guitar via a sampled loop. The recordings were time-aligned perfectly at
the sample level.


No two recordings of any instrument (Whether digital or analogue) played
by a human will ever null completely. Apart from environmental factors
such as the air temperature, the player's will differ timing between the
two recordings.

Getting them as close as you did is actually damn consistent playing.


The recordings weren't played by a human twice. A 10 sec. *recording* of a
guitar DI was played into an amp/cab twice, consecutively, one after the
other, the output of which was recorded and cut up into separate tracks.
Both tracks were time-aligned and the phase inverted on one.
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Ralph Barone[_3_] Ralph Barone[_3_] is offline
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Default Why don't these signals null?

James Price wrote:
On Friday, October 18, 2019 at 3:04:40 PM UTC-5, John Williamson wrote:
On 18/10/2019 17:24, James Price wrote:

These were short (approx. 10 seconds), close-miked recordings, recorded
in two passes, back-to-back using the same mic, through the same cab and fed
a DI guitar via a sampled loop. The recordings were time-aligned perfectly at
the sample level.


No two recordings of any instrument (Whether digital or analogue) played
by a human will ever null completely. Apart from environmental factors
such as the air temperature, the player's will differ timing between the
two recordings.

Getting them as close as you did is actually damn consistent playing.


The recordings weren't played by a human twice. A 10 sec. *recording* of a
guitar DI was played into an amp/cab twice, consecutively, one after the
other, the output of which was recorded and cut up into separate tracks.
Both tracks were time-aligned and the phase inverted on one.


And what happens if due to the vagaries of when you hit the €śPlay€ť button,
the second recording is a half sample out of sync with the first?

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On 19/10/2019 14:22, James Price wrote:

The recordings weren't played by a human twice. A 10 sec. *recording* of a
guitar DI was played into an amp/cab twice, consecutively, one after the
other, the output of which was recorded and cut up into separate tracks.
Both tracks were time-aligned and the phase inverted on one.

It takes a fraction of a millimetre movement or a tiny difference in
atmospheric pressure or temperature to change the time delay between the
speaker and the microphone enough to give the symptoms you describe.

Even a difference in the background noise in the room will do it.

Have you tried normalising the difference signal to hear what it is?

--
Tciao for Now!

John.


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Scott Dorsey Scott Dorsey is offline
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Default Why don't these signals null?

James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that looped part and record the output twice to separate tracks in a DAW, time-align them and invert the phase on one. I know the tracks won't null, but I don't fully understand the why.


They don't sound the same, so why would you expect them to null?

The whole reason you run the signal through a cabinet is to change the
waveform. So don't be surprised when it does just that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Default Why don't these signals null?

On Sunday, October 20, 2019 at 12:31:59 PM UTC-5, Scott Dorsey wrote:
James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that looped part and record the output twice to separate tracks in a DAW, time-align them and invert the phase on one. I know the tracks won't null, but I don't fully understand the why.


They don't sound the same, so why would you expect them to null?

The whole reason you run the signal through a cabinet is to change the
waveform. So don't be surprised when it does just that.


I'm curious why the signals don't null when changes imparted by the cabinet
are controlled for, though? For example, sending a looped guitar DI to
an amp and then running that through an impulse response of a guitar cabinet.
Again, the caveat is that clean tones *will* null, thus I'm referring to
distorted and overdriven tones.
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PStamler PStamler is offline
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Default Why don't these signals null?

On Sunday, October 20, 2019 at 5:13:37 PM UTC-5, James Price wrote:
On Sunday, October 20, 2019 at 12:31:59 PM UTC-5, Scott Dorsey wrote:
James Price wrote:
Let's say I record a DI guitar part into a looper, then re-amp that looped part and record the output twice to separate tracks in a DAW, time-align them and invert the phase on one. I know the tracks won't null, but I don't fully understand the why.


They don't sound the same, so why would you expect them to null?

The whole reason you run the signal through a cabinet is to change the
waveform. So don't be surprised when it does just that.


I'm curious why the signals don't null when changes imparted by the cabinet
are controlled for, though? For example, sending a looped guitar DI to
an amp and then running that through an impulse response of a guitar cabinet.
Again, the caveat is that clean tones *will* null, thus I'm referring to
distorted and overdriven tones.


If I understand what you're describing, you're trying to null a signal that's been run through a guitar cabinet with one that's been run through a *simulation* of a guitar cabinet. Two possible explanations occur to me right off; the first is that simulations aren't perfect. The second is that though the impulse response you're trying to null the cab against may have been made using the same make and model of guitar cabinet, it wasn't made with the *same* guitar cabinet you're trying to null it with. Nor in the same room, nor with the same microphone.
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On Wednesday, October 23, 2019 at 12:35:16 AM UTC-5, PStamler wrote:
If I understand what you're describing, you're trying to null a signal that's
been run through a guitar cabinet with one that's been run through a
*simulation* of a guitar cabinet.


No. In the first instance, I'm referring to nulling a signal that's been sent through a miked guitar cabinet exclusively. However, you can also try sending the signal through an impulse response of a guitar cabinet and it won't null.
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Default Why don't these signals null?

the op is trying to null the 2 re-amped re- recordings to each other.

OP, you got a -30 dB to -50 dB result which is very good.

There are bound to be slight differences in room noise between the two takes. Or a window curtain moved slightly.

Consider that a -40 dB down null means the two signals matched each other to within 1 part in 100.

What did the null signal sound like?

Mark




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Default Why don't these signals null?

James Price wrote:

The recordings weren't played by a human twice. A 10 sec. *recording* of a
guitar DI was played into an amp/cab twice, consecutively, one after the
other, the output of which was recorded and cut up into separate tracks.
Both tracks were time-aligned and the phase inverted on one.


Ahh, I was thinking you were comparing the original DI'ed signal with the
reamped signal.

If you're comparing two reamped signals, the difference is likely the
difference between the two reampings, and the differences are likely
more than 30 dB down.

What is different between the two reampings? Well, the noise is different,
because noise always is (that's the definition of noise... it's not correlated
with signal). Likely the microphone position is a little different (maybe
less than a millimeter), the air currents in the room are a little different
(which is a big deal with a source that has an uneven radiation pattern like
a guitar amp), and if that's a tube amp it's likely warmed up a little more
or a little less and so slightly inconsistent.

You'll know for sure when you listen to the difference signal. Is it all
120 Hz hum? Is it all hiss? Is it correlated enough that you can hear a
guitar note somewhere in it? The best thing about the null test is that you
can use your ears (and an FFT) to figure out what the difference is, as well
as just measuring the absolute difference as a scalar number.

Remember that if you're looking at a difference that is 30 dB down from the
signal, you're seeing a difference of 1/1000th of the signal. It does not
take much.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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On Wednesday, October 23, 2019 at 8:01:59 AM UTC-5, wrote:
the op is trying to null the 2 re-amped re- recordings to each other.

OP, you got a -30 dB to -50 dB result which is very good.

There are bound to be slight differences in room noise between the two takes. Or a window curtain moved slightly.


All recordings are close-miked, so room noise is minimal, and the recordings
are short(ie. approx. 10 secs). More importantly, if room noise were a
factor, the clean guitar recordings would not have nulled.

My best guess is that distortion introduces characteristics that are random
to a degree.
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James Price wrote:
On Wednesday, October 23, 2019 at 8:01:59 AM UTC-5, wrote:
the op is trying to null the 2 re-amped re- recordings to each other.

OP, you got a -30 dB to -50 dB result which is very good.

There are bound to be slight differences in room noise between the two takes. Or a window curtain moved slightly.


All recordings are close-miked, so room noise is minimal, and the recordings
are short(ie. approx. 10 secs). More importantly, if room noise were a
factor, the clean guitar recordings would not have nulled.


What does the residual sound like?

My best guess is that distortion introduces characteristics that are random
to a degree.


What do you mean by "distortion?" Because there are a number of different
things you could mean by that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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