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2 ins -> 3 tracks.....any math geniuses out there?

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Mon Sep 20, 2004 1:15 am Post subject: 2 ins -> 3 tracks.....any math geniuses out there?

Hi everyone! I have an Mbox which has 2 inputs on it. I would like to record bass, guitar and vocals onto 3 seperate tracks. I had an idea to make this possible (with a kind of MS processing I guess), but unfortunatly it didn't go as planned. Here's the plan: 1) Record bass hard left, guitar hard right, and vocals in the center as a stereo track in Pro Tools. 2) Make a copy of this track, mono it, and reverse its phase to cancel out the vocal. 3) Bounce this down to a stereo track of just bass and guitar 4) Import the bass/guitar track as 2 mono tracks panned hard left and right. 5) Reverse their phase against the original track to cancel out the bass and guitar, just leaving the vocal. 6) Bounce down the vocals on their own and import them back into Pro Tools....I would now have bass, guitar, and vocals all on their own seperate tracks. Ok....all good in theory huh? Here's where I went wrong: 1) To start with, the vocal wouldn't cancel, and it took me a several hours to figure out that things panned in the center have a 3dB boost. Easy fix...remeber to attenuate by 3dB when reversing the phase. 2) The vocal finally canceled......but.....the bass and the guitar didn't stay on the left and right, they both came into the center Ok, now I'm stuck. Is there anyone out there that can either make this work for me, or tell me that I am definatly wasting my time and it is simply not possible? Thanks everyone Ryan

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Gidge
Giant Member

Age: 42

Posted: Mon Sep 20, 2004 12:55 pm Post subject:

find out if you can use the analog inputs and the s/pdif inputs simultaneously.....if so you could do the bass direct thru somthing like the J-Station into the S/pdif and then the vocals and guitar separately thru the analog inputs onto 2 separate tracks........ _________________ ********** ******** GidgeMo ******** **********

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Mon Sep 20, 2004 5:19 pm Post subject:

No, you can't use the analogue and s/pdif inputs at the same time

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Gidge
Giant Member

Age: 42

Posted: Mon Sep 20, 2004 6:38 pm Post subject:

honestly, i wouldnt even attempt what you are trying....i would just record the guitar and bass first, then overdub the vocals.....is there a reason you have to record it in one take...... _________________ ********** ******** GidgeMo ******** **********

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Tue Sep 21, 2004 1:14 am Post subject:

Gidge wrote:

is there a reason you have to record it in one take......

Just to see if I can......I like to learn new techniques Very Happy

If George Martin could record Sgt. Pepper on a 4-Track then I don't see any reason why I can't record a live 3 piece band with 2 inputs......I like a challenge Wink

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Gidge
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Age: 42

Posted: Tue Sep 21, 2004 5:54 am Post subject:

of course you can record a live 3 piece with 2 inputs...it wont be to 3 separate tracks so you have to live with the mix you record......theres the challenge...... _________________ ********** ******** GidgeMo ******** **********

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Tue Sep 21, 2004 4:00 pm Post subject:

I know that it's always an option to mix it live.....I'm still convinced that there must be a way to split it into 3 seperate tracks though. All I need to be able to do is remove the center channel (voice) without combining the left and right channels. If the voice was removed, then I could reverse the phase of the bass and guitar against the original stereo file in order to get vocals on their own. Then I would have all 3 instruments on seperate tracks. Anyone know of a good voice canceling plugin?

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gfh
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Joined: 02 Dec 2003
Posts: 3704
Location: Scenic NJ
Age: 34

Posted: Tue Sep 21, 2004 6:25 pm Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

Ryan wrote:

I am definatly wasting my time and it is simply not possible

Sorry man, I think your options are limited to: recording two tracks at a time and then overdubbing, mixing down to two and recording the result, or getting a card with more inputs.

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Wed Sep 22, 2004 1:32 am Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

gfh wrote:

Sorry man, I think your options are limited to: recording two tracks at a time and then overdubbing, mixing down to two and recording the result, or getting a card with more inputs.

Nah....it's all good, I figured out how to do it Very Happy

- Record bass hard left, vocals center, guitars hard right as a stereo track.
- Run the stereo track through an MS matrix: you end up with mono guitar and bass on the left side, and mono guitar bass and vocals on the right.
- Mix down the output of the MS matrix as 2 seperate mono tracks.
- Mute the original stereo track, and pan the 2 new mono tracks to the center.
- Reverse the phase of the left mono track (guitar and bass only), and the guitars and bass will get canceled out all together leaving you with vocals only.
- Bounce down you vocals to their own mono track.
- Now you can get rid of the 2 files from the MS matrix, and unmute the original stereo file.
- Reverse the phase of your vocal only track (panned in the center) and the vocals will disappear from the original stereo track.
- You can then bounce the original stereo track down to 2 mono track (bass and guitar) and get rid of it.

There you have it....getting 3 seperate tracks out of 2 inputs Wink

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gfh
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Joined: 02 Dec 2003
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Location: Scenic NJ
Age: 34

Posted: Wed Sep 22, 2004 6:27 am Post subject:

I stand corrected. Does it still sound ok after you've done all that stuff to it?

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Gidge
Giant Member

Age: 42

Posted: Wed Sep 22, 2004 12:59 pm Post subject:

glad thats working out for ya.....id like to hear the results......free space in the Listening Room....... _________________ ********** ******** GidgeMo ******** **********

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Ryan
Active Member

Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Wed Sep 22, 2004 1:56 pm Post subject:

gfh wrote:

I stand corrected. Does it still sound ok after you've done all that stuff to it?

In theory nothing should change....in practice yes you lose a little bit of level, but it's not to bad

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roman
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Joined: 01 Dec 2003
Posts: 4017
Location: elsewhere
Age: 26

Posted: Thu Oct 21, 2004 6:42 pm Post subject:

I'm with Gidge. I'd like to hear it, it would be cool if you post the result, maybe with a normal recording as a reference. But if you have a second soundcard around somewhere, I would definitely try to get them to work together, I once mysteriously managed to use the sound on board simultaniously with an audigy card. Now I have a m-audio delta 1010 LT. I never thought I would need 10 imputs, Now I could get used to 30

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l0calh05t
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Joined: 10 Dec 2004
Posts: 69

Posted: Fri Dec 10, 2004 3:30 pm Post subject:

isn't this trick similar to what dolby pro logic does?

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l0calh05t
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Joined: 10 Dec 2004
Posts: 69

Posted: Wed Dec 15, 2004 4:41 pm Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

Ryan wrote:

[...]
- Run the stereo track through an MS matrix: you end up with mono guitar and bass on the left side, and mono guitar bass and vocals on the right.
- Mix down the output of the MS matrix as 2 seperate mono tracks.
- Mute the original stereo track, and pan the 2 new mono tracks to the center.
- Reverse the phase of the left mono track (guitar and bass only), and the guitars and bass will get canceled out all together leaving you with vocals only.

Hmm, after thinking about it for a while, how does this work exactly?

IIRC an MS Matrix produces the Sum and the Difference of the input signals right? Now this means that the phase on one of the instruments in the instruments only would have inverted phase, now, if you subtract (invert phase and add) this from the Sum don't you just get one of the channels at double volume? Or am I missing something here or got it completely wrong?

To explain:

A=Guitar+Vocals
B=Bass+Vocals

A+B=Guitar+Bass+2*Vocals
A-B=Guitar-Bass

(A+B)-(A-B)=2*Bass+2*Vocals

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Fri Dec 17, 2004 5:51 pm Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

l0calh05t wrote:

When something is panned center it should automatically be attenuated by 3dB, so you don't get 2x the vocals.

A= Guitar + (-3db) Vocals
B= Bass + (-3db) Vocals

A+B = Guitar + Bass + Vocals
A-B = Guitar + Bass
(A-B)-(A+B) = Vocals
Stereo AB - Vocals = Guitar (left) + Bass (right)

Give it a try....It does work Very Happy

P.S
Yes it is very similar to the way Dolby Pro Logic works I think

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l0calh05t
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Joined: 10 Dec 2004
Posts: 69

Posted: Sat Dec 18, 2004 3:20 am Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

Ryan wrote:

l0calh05t wrote:

P.S
Yes it is very similar to the way Dolby Pro Logic works I think

If A = Guitar + (-3db)Vocals and B = Bass + (-3db) Vocals

why should A-B = Guitar + Bass??? That doesn't really make sense... (which is what i was talking about, not the 2*Vocals which wouldn't really matter)

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Sat Dec 18, 2004 4:42 pm Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

l0calh05t wrote:

When you subtract A from B only the things which are common in both signals will cancel (ie. vocals).
If you have 3 apples, and you subtract 3 oranges, how many apples do you have?......Still 3.

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l0calh05t
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Joined: 10 Dec 2004
Posts: 69

Posted: Sat Dec 18, 2004 5:05 pm Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

Ryan wrote:

l0calh05t wrote:

When you subtract A from B only the things which are common in both signals will cancel (ie. vocals).
If you have 3 apples, and you subtract 3 oranges, how many apples do you have?......Still 3.

Yes, but I have -3 oranges (the Bass signal has inverted phase) and if i now add 3 oranges i have none.

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Sun Dec 19, 2004 4:25 am Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

l0calh05t wrote:

Yes, but I have -3 oranges (the Bass signal has inverted phase) and if i now add 3 oranges i have none.

Inverting the bass signal does not make it disapear. Adding an inverted bass signal to the original bass signal will cancel, but we're not doing that. We are adding an inverted bass signal to a guitar signal, therefore neither cancel.
I think your getting a bit confused as to what is actually going on;

Channel A is a mix of guitar and vocals (no bass).
Channel B is a mix of bass and vocals (no guitar).
If you invert the polarity of channel B you get inverted bass and vocals (which sounds no different to the original channel B).
If you now add channel A to the polarity inverted B, the vocal is positive in A, but negative in B, and therefore cancels. Nothing happens to the bass or guitar.

Understand?.....I can't think of a more simple way to explain this. Why don't you give it a try?

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l0calh05t
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Joined: 10 Dec 2004
Posts: 69

Posted: Sun Dec 19, 2004 4:54 am Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

Ryan wrote:

l0calh05t wrote:

Yes, but I have -3 oranges (the Bass signal has inverted phase) and if i now add 3 oranges i have none.

uh, i don't think you understood what i meant:

In the A-B signal the Bass part will also have inverted polarity (this should be obvious, as you can't invert the B signal without inverting Vocals AND Bass)

Now in A+B the Bass does not have inverted polarity (obviously)

So now if you add A+B and A-B Bass will cancel out

Oh, and i tried it with some test tones, and it didn't work.

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Ryan
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Joined: 13 Feb 2004
Posts: 238
Location: Sydney
Age: 27

Posted: Mon Dec 20, 2004 1:22 am Post subject: Re: 2 ins -> 3 tracks.....any math geniuses out there?

l0calh05t wrote:

Ok, I understand what your saying now, and you are correct. Sorry.
I did miss a couple of steps, here's a little picture i made to explain things a bit better:
G = guitar, B = Bass, V = Vocals. There arrows indicate the polartity. Sory if it a bit hard to follow.
Once you have bass on it's own you can easily get vocals on their own, and then guitar.

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