Stereo input as balanced input

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Stereo input as balanced input

Torquil Macdonald Sørensen
Hi all!

How can I use my computer sound card stereo input as a balanced input with jackd?

I have a passive DI box that generates a balanced signal and I connect this to
my sound card input using a stero 3.5mm plug. All that is needed is for some
jack-compatible software to invert one side of the signal and then sum the two
sides together to a mono signal. However, I am having trouble finding such
software. Can anyone point me in the right direction?

Or should Alsa do this?

I'm on Debian Sid, and this is an Asus laptop with the following sound card:

nVidia Corporation High Definition Audio Controller (rev a1)

I really need to reduce noise as much as possible since it is amplified a lot
through guitar distortion effects (rakarrack/guitarix), so I thought about
exploiting the balanced input. Although I'm not sure it will have a significant
effect. It depends if the noise added by the sound card to the two channels is
correlated or not...

Torquil
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Re: Stereo input as balanced input

Ralf Mardorf
On Wed, 2010-06-23 at 20:12 +0200, Torquil Macdonald Sørensen wrote:

> Hi all!
>
> How can I use my computer sound card stereo input as a balanced input with jackd?
>
> I have a passive DI box that generates a balanced signal and I connect this to
> my sound card input using a stero 3.5mm plug. All that is needed is for some
> jack-compatible software to invert one side of the signal and then sum the two
> sides together to a mono signal. However, I am having trouble finding such
> software. Can anyone point me in the right direction?
>
> Or should Alsa do this?
>
> I'm on Debian Sid, and this is an Asus laptop with the following sound card:
>
> nVidia Corporation High Definition Audio Controller (rev a1)
>
> I really need to reduce noise as much as possible since it is amplified a lot
> through guitar distortion effects (rakarrack/guitarix), so I thought about
> exploiting the balanced input. Although I'm not sure it will have a significant
> effect. It depends if the noise added by the sound card to the two channels is
> correlated or not...
>
> Torquil

Using this kind of phasing for pickups, 2 coils, directly on your Guitar
will reduce noise, even without a phase switch, but if you phase a
stereo signal and sum it to a mono signal, you will get a very, very
unwanted effect. There will be nearly no sound anymore! Btw. balanced or
unbalanced for a guitar doesn't make a difference. Your coils are
antennas for electric smog.

Ralf


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Re: Stereo input as balanced input

Ralf Mardorf
In reply to this post by Torquil Macdonald Sørensen
PS:

I guess you don't understand what balanced does mean.

Here are some hints to reduce noise for guitars.

If you are using single coils pick ups, you'll have a lot of trouble with noise in a computer studio.

Use two single coils and scale down the one you won't have for the sound. This will reduce noise.

You can add a phase switch to the middle pick up of a Stratocaster, but this won't reduce the noise more than using two pick ups without such a switch, you only would get less bass.

Add ground to the strings and use your body to shield electric smog.

Use humbuckers, the name is self-explaining. A humbucker is using two coils in one pick up.

I'm a single coil player and I use my body to shield electric smog. Sometimes I'm using two single coils, were one coil is screwed down. I never use the phase switch.
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Re: Stereo input as balanced input

Arnold Krille-3
On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
> PS:
>
> I guess you don't understand what balanced does mean.

I guess you haven't read the original mail.

He uses a DI-Box to balance the signal. And now he wants to get that symmetric
signal into the pc via a consumer-soundcard. Mis-using the stereo-input and
inverting one phase might actually work. I would test that with either jack-
rack (there are some volume controls that allow values, that is factor between
-1 and 1, where -1 would do the inversion). Or with a small pd script.

But is it worth it?

As Ralf rightly said, the noise of an electric guitar is not added in the
cable but in the pickups and the (pre-)amps. If balanced cables would help in
that, guitarists would use balanced cables to connect their guitar to the amp.

I would use a small usb or firewire interface that has hi-Z inputs to directly
connect your guitar...

Have fun,

Arnold

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Re: Stereo input as balanced input

Ralf Mardorf
On Wed, 2010-06-23 at 20:43 +0200, Arnold Krille wrote:
On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
> PS:
> 
> I guess you don't understand what balanced does mean.

I guess you haven't read the original mail.
[...]
If balanced cables would help in 
that, guitarists would use balanced cables to connect their guitar to the amp.

I was referring to this ;).

I would use a small usb or firewire interface that has hi-Z inputs to directly 
connect your guitar...

Some kind of pre-amp is needed, if you directly connect the guitar to your sound card. I'm using a mixing console. If you don't have a mixer, use an effect device, e.g an overdrive, in addition to the famous Rakarrack, e.g. the Boss Turbo OverDrive OD-2 is very good and won't hurt the Rakarrack's sound.

:)
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Re: Stereo input as balanced input

Torquil Macdonald Sørensen
In reply to this post by Arnold Krille-3
On 23/06/10 20:43, Arnold Krille wrote:

> On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
>> PS:
>>
>> I guess you don't understand what balanced does mean.
>
> I guess you haven't read the original mail.
>
> He uses a DI-Box to balance the signal. And now he wants to get that symmetric
> signal into the pc via a consumer-soundcard. Mis-using the stereo-input and
> inverting one phase might actually work. I would test that with either jack-
> rack (there are some volume controls that allow values, that is factor between
> -1 and 1, where -1 would do the inversion). Or with a small pd script.
>
> But is it worth it?
>
> As Ralf rightly said, the noise of an electric guitar is not added in the
> cable but in the pickups and the (pre-)amps. If balanced cables would help in
> that, guitarists would use balanced cables to connect their guitar to the amp.
>
> I would use a small usb or firewire interface that has hi-Z inputs to directly
> connect your guitar...
>
> Have fun,
>
> Arnold

Thanks Arnold, your summary of my intents/setup is correct. The DI box creates
the balanced signal and this goes into the stereo input. Up to now I have used
only the left side of this, since using both would cancel out most of the sound.

I'm 90% sure most of the noise I'm getting is not from the guitar. Playing into
the computer is a hundred times noisier than when I use my tube guitar amp. So
I'm pretty sure this noise is mostly created in the sound card, although I
haven't yet tried to move the guitar away from the laptop.... Just though of
that now as I write :-)

Sure, I can improve it by using a better audio interface, and I have tried it
with success sing a Tonelab ST USB audio interface which is also a guitar FX
processor/modeller. But I wanted to umake this work with my simple passive DI
box for a simpler setup (fewer cables).

My hope was that exploiting the balanced signal might help me reduce noise
created in the sound card, but as I mentioned I'm not 100% sure it will have a
noticeable effect, since it only works when the noise imparted on the signal is
the same in both channels, and that might not be the case the this noise.

Thanks for the jack-rack suggestion, I will investigate it and report back with
results.

Torquil
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Re: Stereo input as balanced input

Arnold Krille-3
Hi,

On Wednesday 23 June 2010 20:59:36 Torquil Macdonald Sørensen wrote:
> On 23/06/10 20:43, Arnold Krille wrote:
> I'm 90% sure most of the noise I'm getting is not from the guitar. Playing
> into the computer is a hundred times noisier than when I use my tube
> guitar amp. So I'm pretty sure this noise is mostly created in the sound
> card, although I haven't yet tried to move the guitar away from the
> laptop.... Just though of that now as I write :-)

If it gets better when you move the guitar away from the laptop, I am pretty
sure this effect is because the guitar-pickups pick up less electromagnetic
noise from the laptop, not the laptop picking up less noise from the guitar.
And I am pretty sure that a balanced cable will not help you any in this
setup. A balanced connection will only get interesting when guitar and
computer are more then five meters apart...

> Sure, I can improve it by using a better audio interface, and I have tried
> it with success sing a Tonelab ST USB audio interface which is also a
> guitar FX processor/modeller. But I wanted to umake this work with my
> simple passive DI box for a simpler setup (fewer cables).

Simplier setup in this case means worse sound. Not only are the ad-converters
of the built-in soundcard worse then most external devices, you are also
giving the guitar a wrong impedance on the other end of the cable...

> My hope was that exploiting the balanced signal might help me reduce noise
> created in the sound card, but as I mentioned I'm not 100% sure it will
> have a noticeable effect, since it only works when the noise imparted on
> the signal is the same in both channels, and that might not be the case
> the this noise.

If the noise _really_ comes from the computer, it will not cancel out, it will
increase as both channels' noise is independent of the other and thus not
correlated.

Have fun,

Arnold

PS: Why is this question on jack-devel and not on lau where it would belong?

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Re: Stereo input as balanced input

Ralf Mardorf
On Wed, 2010-06-23 at 21:19 +0200, Arnold Krille wrote:

> Hi,
>
> On Wednesday 23 June 2010 20:59:36 Torquil Macdonald Sørensen wrote:
> > On 23/06/10 20:43, Arnold Krille wrote:
> > I'm 90% sure most of the noise I'm getting is not from the guitar. Playing
> > into the computer is a hundred times noisier than when I use my tube
> > guitar amp. So I'm pretty sure this noise is mostly created in the sound
> > card, although I haven't yet tried to move the guitar away from the
> > laptop.... Just though of that now as I write :-)
>
> If it gets better when you move the guitar away from the laptop, I am pretty
> sure this effect is because the guitar-pickups pick up less electromagnetic
> noise from the laptop, not the laptop picking up less noise from the guitar.

Correct! And as you Arnold said before. He needs other inputs, e.g. a
pre-amp. And in addition my hint to give ground to the strings and use
the body as shield or to use two coils are the usual way to avoid noise.

Torquil, you tube amp has got a pre-amp. I guess this is your major
problem, even the coils are a minor issue.

> And I am pretty sure that a balanced cable will not help you any in this
> setup.

I'm sure for 100%.

> A balanced connection will only get interesting when guitar and
> computer are more then five meters apart...

Even not than. A guitar is an antenna, because of the coils.

> > Sure, I can improve it by using a better audio interface, and I have tried
> > it with success sing a Tonelab ST USB audio interface which is also a
> > guitar FX processor/modeller. But I wanted to umake this work with my
> > simple passive DI box for a simpler setup (fewer cables).
>
> Simplier setup in this case means worse sound. Not only are the ad-converters
> of the built-in soundcard worse then most external devices, you are also
> giving the guitar a wrong impedance on the other end of the cable...

Pre-amp or mixing console or a simple effect device for the floor would
fix that.

> > My hope was that exploiting the balanced signal might help me reduce noise
> > created in the sound card, but as I mentioned I'm not 100% sure it will
> > have a noticeable effect, since it only works when the noise imparted on
> > the signal is the same in both channels, and that might not be the case
> > the this noise.
>
> If the noise _really_ comes from the computer, it will not cancel out, it will
> increase as both channels' noise is independent of the other and thus not
> correlated.
>
> Have fun,
>
> Arnold
>
> PS: Why is this question on jack-devel and not on lau where it would belong?

Because he hopes to get information about a phase switch for JACK.

Cheers!

Ralf

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Re: Stereo input as balanced input

Ralf Mardorf
In reply to this post by Arnold Krille-3
Sorry for the PS, but resumed:

> > I'm 90% sure most of the noise I'm getting is not from the guitar. Playing
> > into the computer is a hundred times noisier than when I use my tube
> > guitar amp.

> you are also
> giving the guitar a wrong impedance on the other end of the cable...

There's absolutely no doubt about what will cause the noise!
Let's avoid the technical term 'impedance'. Any kind of more or less
good pre-amplification will solve this issue. Not only a pre-amp, a
mixer or an effect, but also some kinds of active pick ups. While an
effect or active pick ups aren't a guarantee to fix this issue, a mixing
console or a pre-amp by guarantee will fix it.

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Re: Stereo input as balanced input

Tim-2
In reply to this post by Ralf Mardorf
On June 23, 2010 02:52:03 pm Ralf Mardorf wrote:

> On Wed, 2010-06-23 at 20:43 +0200, Arnold Krille wrote:
> > On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
> > > PS:
> > >
> > > I guess you don't understand what balanced does mean.
> >
> > I guess you haven't read the original mail.
> > [...]
> > If balanced cables would help in
> > that, guitarists would use balanced cables to connect their guitar to the
> > amp.
>
> I was referring to this ;).
>
> > I would use a small usb or firewire interface that has hi-Z inputs to
> > directly connect your guitar...
>
> Some kind of pre-amp is needed, if you directly connect the guitar to
> your sound card. I'm using a mixing console. If you don't have a mixer,
> use an effect device, e.g an overdrive, in addition to the famous
> Rakarrack, e.g. the Boss Turbo OverDrive OD-2 is very good and won't
> hurt the Rakarrack's sound.
>
> :)

Preamp? No, that just adds more (electronic) noise to be amplified
 by the distortion effects later.
I have no trouble with my Radial Engineering passive DI box balanced
 output going into my MAudio Delta-1010 sound card's balanced input.
The level is just fine as it is.

Using a mixing board to preamp guitar is not good either unless the
 particular chosen input has a very high impedance of around 1MOhm.
Anything lower, and the impedance will muddy (low pass filter)
 the guitar sound because of the loading of the guitar's
 12KOhm / 6KOhm coils.

Interesting idea of feeding into stereo inputs and summing later.
But I'm not sure the effect of the sound card's relatively higher
 input impedances of around 10-20 KOhm.
Shouldn't they be low impedance paths to ground for balanced
 type signals? Around 100 Ohms?

You can find a LADSPA effect plugin to invert one channel.
Fire up a LADSPA host like JackRack and try to work with that.
Or try MusE, Ardour or Rosegarden to host.

Tim.

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Re: Stereo input as balanced input

Paul Davis
On Wed, Jun 23, 2010 at 4:18 PM, Tim E. Real <[hidden email]> wrote:

> You can find a LADSPA effect plugin to invert one channel.
> Fire up a LADSPA host like JackRack and try to work with that.
> Or try MusE, Ardour or Rosegarden to host.

ardour can do polarity inversion all by itself, without a plugin.
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Re: Stereo input as balanced input

Ralf Mardorf
In reply to this post by Tim-2
On Wed, 2010-06-23 at 16:18 -0400, Tim E. Real wrote:
On June 23, 2010 02:52:03 pm Ralf Mardorf wrote:
> On Wed, 2010-06-23 at 20:43 +0200, Arnold Krille wrote:
> > On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
> > > PS:
> > >
> > > I guess you don't understand what balanced does mean.
> >
> > I guess you haven't read the original mail.
> > [...]
> > If balanced cables would help in
> > that, guitarists would use balanced cables to connect their guitar to the
> > amp.
>
> I was referring to this ;).
>
> > I would use a small usb or firewire interface that has hi-Z inputs to
> > directly connect your guitar...
>
> Some kind of pre-amp is needed, if you directly connect the guitar to
> your sound card. I'm using a mixing console. If you don't have a mixer,
> use an effect device, e.g an overdrive, in addition to the famous
> Rakarrack, e.g. the Boss Turbo OverDrive OD-2 is very good and won't
> hurt the Rakarrack's sound.
>
> :)

Preamp? No, that just adds more (electronic) noise to be amplified 
 by the distortion effects later.
I have no trouble with my Radial Engineering passive DI box balanced 
 output going into my MAudio Delta-1010 sound card's balanced input.
The level is just fine as it is. 

Using a mixing board to preamp guitar is not good either unless the 
 particular chosen input has a very high impedance of around 1MOhm.
Anything lower, and the impedance will muddy (low pass filter) 
 the guitar sound because of the loading of the guitar's 
 12KOhm / 6KOhm coils.

Interesting idea of feeding into stereo inputs and summing later.
But I'm not sure the effect of the sound card's relatively higher
 input impedances of around 10-20 KOhm.
Shouldn't they be low impedance paths to ground for balanced 
 type signals? Around 100 Ohms?

You can find a LADSPA effect plugin to invert one channel.
Fire up a LADSPA host like JackRack and try to work with that.
Or try MusE, Ardour or Rosegarden to host.

Tim.

Tim, we aren't talking about high quality, clean audio signals, but dirty faithful guitar amp simulated sounds. Regarding to the bad impedance, there is to less signal = to much noise. Any pre-amplification will fix this. Around 30 years of pro-audio engineering teach, resp. experienced me regarding to this issue. I recorded guitars for professional productions directly by the mixing console when this was exotic. Today it's common to do this, since there are all those cabinet emulations. E-guitars are metal-strings recorded by a magnet coil. Forget about engineering theory. More power and everything is fine ;).
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Re: Stereo input as balanced input

Fons Adriaensen-2
In reply to this post by Torquil Macdonald Sørensen
On Wed, Jun 23, 2010 at 08:12:14PM +0200, Torquil Macdonald Sørensen wrote:

> How can I use my computer sound card stereo input as a balanced input with jackd?

Don't.
 
> I have a passive DI box that generates a balanced signal and I
> connect this to my sound card input using a stero 3.5mm plug. All
> that is needed is for some jack-compatible software to invert one
> side of the signal and then sum the two sides together to a mono
> signal. However, I am having trouble finding such software. Can
> anyone point me in the right direction?

If your DI box is really passive (which means it's just a transformer)
this is not going to work very well - as the output of your DI box is
floating (not connected to ground) each of the two inputs will see
the input impedance of the other in series. It's likely to make things
worse.

Anyway a real balanced input does the 'subtraction' in the analog
domain, not after DA conversion and possibly unmatched gains.

You have to options:

- Make a cable ending in a mono 3.5mm plug (i.e. just TS, no R),
  connecting one of two balanced signals to ground *at the end*,
  i.e. in the 3.5mm plug.

- Get a decent soundcard.

Ciao,

--
FA

O tu, che porte, correndo si ?
E guerra e morte !
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Re: Stereo input as balanced input

Ralf Mardorf
On Wed, 2010-06-23 at 22:47 +0200, [hidden email] wrote:

> On Wed, Jun 23, 2010 at 08:12:14PM +0200, Torquil Macdonald Sørensen wrote:
>
> > How can I use my computer sound card stereo input as a balanced input with jackd?
>
> Don't.
>  
> > I have a passive DI box that generates a balanced signal and I
> > connect this to my sound card input using a stero 3.5mm plug. All
> > that is needed is for some jack-compatible software to invert one
> > side of the signal and then sum the two sides together to a mono
> > signal. However, I am having trouble finding such software. Can
> > anyone point me in the right direction?
>
> If your DI box is really passive (which means it's just a transformer)
> this is not going to work very well - as the output of your DI box is
> floating (not connected to ground) each of the two inputs will see
> the input impedance of the other in series. It's likely to make things
> worse.

101% ACK!

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Re: Stereo input as balanced input

Torquil Macdonald Sørensen
In reply to this post by Arnold Krille-3
On 23/06/10 20:43, Arnold Krille wrote:

> On Wednesday 23 June 2010 20:33:37 Ralf Mardorf wrote:
>> PS:
>>
>> I guess you don't understand what balanced does mean.
>
> I guess you haven't read the original mail.
>
> He uses a DI-Box to balance the signal. And now he wants to get that symmetric
> signal into the pc via a consumer-soundcard. Mis-using the stereo-input and
> inverting one phase might actually work. I would test that with either jack-
> rack (there are some volume controls that allow values, that is factor between
> -1 and 1, where -1 would do the inversion). Or with a small pd script.
>
> But is it worth it?
>
> As Ralf rightly said, the noise of an electric guitar is not added in the
> cable but in the pickups and the (pre-)amps. If balanced cables would help in
> that, guitarists would use balanced cables to connect their guitar to the amp.
>
> I would use a small usb or firewire interface that has hi-Z inputs to directly
> connect your guitar...
>
> Have fun,

Thanks! Actually, it worked better than I expected.

Since the topic got a few responses I should clarify a bit before I mention my
results. I'll just do that here instead of answering the other responses. I hope
that's fine?

I didn't mean to use this method for anything where sound quality was important
att all. After all, I have other equipment for that, and even a USB audio
interface. However, it requires a separate power supply, so I wanted to improve
my "guitar straight into laptop" results by adding the passive DI box.

I knew all along that there would be a great impedance mismatch between the
guitar and the line in/mic in on my sound card. So I though of using my DI box.
Actually, it had an obvious advantage that I noticed immediately. Originally.
turning the volume knob on the guitar generated some very annoying noises
through the computer sound card. This is now gone thanks to the DI box.

Then I though that if some of the noise imparted on the signal within the sound
card was the same, I should be able to cancel it using this "balanced approach".
It seems to me that this was correct:

When I send my "balanced signal" through jack-rack, using a Steve Harris LADSPA
plugin called "Inverter", and inverting only one channel, the noise is actually
reduced compared to using only one side of the incoming signal as I did before!
When I flip between the two configurations it is easy to hear that the noise is
reduced. It doesn't go away completely of course, but is reduced by a notiseable
amount.

If anyone is interested, the DI box is a "Leem Direct Box, DR-40". My guitar
goes into the "In Inst High 2" and the balanced signal goes out of the "Low 2
Output" XLR plug. The stereo cable going from the XLR plug is connected to the
3.5mm plug in the normal fashion.

Thanks to all that have commented one this topic! I'll have to go through it
again and check out the interesting points, but now I'm going to see about
firing up Rakarrack again (I have now been comparing noise levels without doing
any other sound processing).

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