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.

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.

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.

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 “Play� button,
the second recording is a half sample out of sync with the first?

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.

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."

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.

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.

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.

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