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How to split guitar signal?

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How to split guitar signal?

Postby gingertimmins » Sat Sep 21, 2019 10:29 pm

Hello recording gurus,
I’m overdubbing bass and guitars this week with my band and the plan is to capture a mic’d Amp and DI at the same time. Trouble is I don’t have a DI box/reamp box or anything like that.
What would be the easiest way to do so?

I’ve heard of using a stereo guitar pedal, sending one output to the amp and the other to the interface. Any real value in that?
I also have an alesis mixer (multimix usb?)
I thought of plugging the guitar into that and sending one output channel to amp and one to the interface but then I thought about instrument and line level and then I gave up thinking about it as I don’t really understand it!

Can anyone give me some pointers and possibly an explanation of the levels thing?

Cheers,
Chris
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Re: How to split guitar signal?

Postby Hugh Robjohns » Sat Sep 21, 2019 11:46 pm

Buy a decent active DI box.

It's the right tool for the job, and it will be useful many more times in the future, so a worthwhile investment.

The most cost-effective and best sounding option i know would be the Orchid electronics Classic DI box. Costs about £40. https://www.soundonsound.com/reviews/orchid-electronics-di-boxes

However there are plenty of other active DI boxes around with prices up to about £200...
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Re: How to split guitar signal?

Postby ef37a » Sun Sep 22, 2019 5:30 am

As Hugh says, the very best way is a good quality active DI but you could try as basic as this..

https://tinyurl.com/y3wamdwl

Split the signal from the guitar or better, from the output of a pedal (but not one of the daft "True Bypass" types) .
Ok, not ideal because you halve the load on the guitar's electronics (but not from a proper pedal) and add extra cable capacitance.
You also run the risk of hum loops as you now have two pieces of kit with their earths tied together but there are solutions to that. Usually!

Forgive me Chris but the very fact that you ask this question tells me you have very little electrical knowledge? If so you will find that a constant stumbling block working in music with amplification and especially recording.

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Re: How to split guitar signal?

Postby Sam Spoons » Sun Sep 22, 2019 11:11 am

+1 for the orchid Classic DI http://orchid-electronics.co.uk/classic_DI.htm.

RE- Levels, there are four 'standard' levels you will commonly encounter playing in a rock band (simplified explanation) :-

1, 'pro' line level, the strongest and what 'proper' power amps and powered speakers expect.
2, 'consumer line level' what domestic CD players etc. output (usually on RCA/phono connectors).
3, 'instrument level, roughly what an active electric guitar or keyboard puts out.
4, 'mic' level, the lowest and, usually, by a big margin.

1 and 2 are precise standards at +4dBU and -10dBV (note different units, they are roughly 13dB different). The latter two vary considerably, ribbon mics have very low output, phantom powered capacitors pretty high, 'vintage single coil pickups are much lower output than 'hot' humbuckers.

The upshot is that you can plug a mic into a guitar amp and it will probably work but if you plug it into a 'pro line input' it won't be loud enough.

HTH
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Re: How to split guitar signal?

Postby The Elf » Sun Sep 22, 2019 11:36 am

My choice was the Little Labs Red Eye, which gives you a DI and a re-amper in one box. The later '3D' model lets you switch from one to the other with the push of a button, as well as enabling both passive and active use. All of the ins/outs are labelled clearly and simply, so you don't need to know much to use it.

But from what you're saying it's probably a bit late in the day to offer such buying advice.
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Re: How to split guitar signal?

Postby Hugh Robjohns » Sun Sep 22, 2019 12:01 pm

Sam Spoons wrote:1 and 2 are precise standards at +4dBU and -10dBV (note different units, they are roughly 13dB different).

I agree with your outline Sam, but If I may don the pedant's hat briefly?

It's a lower-case 'u' in dBu (the 'u' signifying 'unterminated', in fact).

And the difference between nominal 'pro' levels at 4dBu and 'domestic' levels at -10dBV is closer to 12dB than 13.

The actual numbers are: -10dBV = 0.316Vrms and +4dBu = 1.228Vrms, so the difference between them in decibels is 11.8dB. Therefore, a domestic device puts out and expects around a quarter of the signal amplitude compared to a professional device!

When teaching BBC soundies, the studio consoles generally changed preamp gain in 6dB steps, so boosting a domestic player to conform with a pro line level expectations was 'two clicks to the right'! :-)

The 11.8dB number is seered into my mind after I was taken to task in a formal letter of complaint from a Dr N Sackman many years ago. He complained about a review in which I stated that a button switched between nominal +4dBu and -10dBV output modes by introducing a 14dB pad...

He was quite irate that I apparently didn't understand the significance of the suffixes and had therefore described the pad's attenuation value incorrectly... In fact, I had actually measured the output levels from the device in the two modes, and in the review I was pointing out the manufacturer's (very minor) miscalculation! The domestic output was technically about 2dB lower than it should have been -- although at least the error was on the safe side!

Anyway, the difference really is 11.8dB, or 12dB between friends! :lol:
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Re: How to split guitar signal?

Postby gingertimmins » Sun Sep 22, 2019 12:11 pm

Thanks for the suggestions and education everyone.
I’d be the first to admit that I don’t fully understand electronics and that’s why I come to you good folk!

A Di box is on the purchase list but this month I can’t warrant the spend as I’ve already spent my allowance on xlr cables and mic stands.

Where we rehearse and record is part of a commercial studio complex so there’s a very good chance I could borrow one from the main studio for this weeks session. It seems that it’s the proper solution.

Thanks for the help guys!
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Re: How to split guitar signal?

Postby Hugh Robjohns » Sun Sep 22, 2019 12:14 pm

:thumbup:
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Re: How to split guitar signal?

Postby Sam Spoons » Sun Sep 22, 2019 12:29 pm

Hugh Robjohns wrote:Anyway, the difference really is 11.8dB, or 12dB between friends! :lol:

:D :blush:
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Re: How to split guitar signal?

Postby ef37a » Sun Sep 22, 2019 12:48 pm

Sam Spoons wrote:
Hugh Robjohns wrote:Anyway, the difference really is 11.8dB, or 12dB between friends! :lol:

:D :blush:

Friends always Sam.. But! The CD was perhaps a poor choice to illustrate domestic levels? They usually run about 2V at full output to accomodate the vast dynamic range, that's +8dBu. I know of at least one pre amp design that incorporates a 16dB attenuator in the CD input to bring the signal into line with those from Tuner and Tape and the output of the phono pre amp.

But then domestic levels ARE all over the shop! I have just checked the output of my Sony Dolby S cassette deck (evaluating some cheap Maxell cassettes) and it delivers 369mV at 333Hz for Dolby level*. That is -6.44 dBu.

Neg 10, 316mV is touted for home kit but hi fi was always reckoned to operate at around 100 to 150mV.

*VERY hard to set to DL because the pot does not have infinite resolution and the LED bars are rather unstable.

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Re: How to split guitar signal?

Postby Hugh Robjohns » Sun Sep 22, 2019 1:10 pm

ef37a wrote:The CD was perhaps a poor choice to illustrate domestic levels? They usually run about 2V at full output to accomodate the vast dynamic range, that's +8dBu.

Not actually such a silly idea, Dave! The -10dBV level is the nominal alignment level -- the domestic 0VU equivalent, so the 2V peak level standard for CD players allows 16dB of headroom above that alignment level which is entirely reasonable and directly comparable to the headroom margin adopted by most current (loudness normalised) music streaming services and the AES streaming standard.

I know of at least one pre amp design that incorporates a 16dB attenuator in the CD input to bring the signal into line with those from Tuner and Tape and the output of the phono pre amp.

The problem, as always, was the adoption and then abuse of peak normalisation in mastering commercial CDs, where the intended headroom margin -- which is present in cassette and vinyl formats, of course -- was effectively removed.

The image below compares the meters on one of the first CD mastering recorders (the PCM1610), compared to the later PCM1630. It clearly shows that the original concept was very analogue-like, with a nominal 'zero' 20dB below digital clipping. It was the subsequent switch to a scale descending from 0dBFS that encouraged the peak-normalisation era... :-(

Sony PCM1610_1630 Meter compare.jpg


Neg 10, 316mV is touted for home kit but hi fi was always reckoned to operate at around 100 to 150mV.

As I'm sure you know, that comes from the 'previous' DIN standard widely employed across Europe in the valve era. The standard defined a current source for the output such that the actual signal voltage was determined by the input impedance of the receiving device (1mV/1k Ohm). As most products settled on 100K as the input impedance, the nominal signal voltage was 100mV rms.

When the Japanese made big inroads into consumer hi-fi, they did so with a more conventional matched voltage interface format, settling on the 316mV (-10dBV) standard which has become ubiquitous.
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Re: How to split guitar signal?

Postby ef37a » Sun Sep 22, 2019 1:52 pm

Hugh, did not call Sam's example "silly"!

Back in the day I modded countless stereo systems for people who had bought a CD player, plugged it into the AUX input and nearly lost their speakers! Those four wee resistors bought me many pint!

Yes, I am aware of the DIN standard and the Japanese might have gone away from the constant current system (which made sense with valves) but they kept pretty much the same signal voltages.
A random swoop on a couple of Hi Fi News copies gets me a Toshiba SP514 4ch amp with Tape AUX Tuner op level at 135mV.
A Rogers Ravenbourne amp is a bit higher at 230mV...As I said, domestic levels were all over the shop.

I have no idea of the levels in modern hi fi separates? Have to see what I can find but you know what specifications are like in THAT world Hugh!

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Re: How to split guitar signal?

Postby Hugh Robjohns » Sun Sep 22, 2019 2:10 pm

ef37a wrote:Hugh, did not call Sam's example "silly"!

:D I know... I was just saying having such an apparently high output level was not a silly idea -- it's just the difference between quoting nominal and peak levels.

I have no idea of the levels in modern hi fi separates?

It's still pretty variable, I think. I was recently checking the adjustable input sensitivity of a Meridian 502 preamp I have, and although that expects a nominal input of 150mV, it can accommodate a +/-15dB range, which means as low as 27mV and as high as 840mV!
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Re: How to split guitar signal?

Postby firsly » Mon Sep 23, 2019 3:27 pm

I actually had almost the same problem and you really helped me, thank you guys!
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Re: How to split guitar signal?

Postby gingertimmins » Mon Sep 23, 2019 8:55 pm

I’ve actually got another question now that I have gotten my hands on a Di box....
I’ve read that due to the tiny time difference between mic’d signal and Di signal that I need to phase align the two.
In one article it said to use a delay plug-in on he mic’d signal, set to around 2ms. I assume this would be set to 100% wet so that I’m hearing only the delay and none of the original audio?
Or I could nudge it manually and align the waveforms.
I understand that this is likely to be more important in the bass than it is the guitar but is there any truth in this at all are the aforementioned methods the way to deal with it?

I’m using cubase elements 9.5 which has a pretty basic tool kit so if it can be done with just the basics that would be cool!
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Re: How to split guitar signal?

Postby Wonks » Mon Sep 23, 2019 9:06 pm

Manually nudge it. A lot quicker and you know it'll be right. 2ms is for a mic 2 feet away from the speaker. Close mic the bass and it will be way less than a 1ms delay.
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Re: How to split guitar signal?

Postby gingertimmins » Mon Sep 23, 2019 9:08 pm

Wonks wrote:Manually nudge it. A lot quicker and you know it'll be right.
That’s what I thought. Thanks for confirming that it likely needs doing!
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Re: How to split guitar signal?

Postby Hugh Robjohns » Mon Sep 23, 2019 9:51 pm

gingertimmins wrote:I’ve read that due to the tiny time difference between mic’d signal and Di signal that I need to phase align the two.

You don't have to phase-align them...

If you choose to mix the DI signal and mic'd signal together (at similar levels) then the small timing difference between them may result in some comb-filtering colouration. But you may well like the effect, so I'd suggest having a listen first before dialling in the delay.

In one article it said to use a delay plug-in on the mic’d signal, set to around 2ms.

Er... No! :?

The DI signal is the direct electrical sound, arriving at (almost) the speed of light. The mic'd signal will be slightly late because of the much slower speed of sound through air -- the rule of thumb is 1ms per foot. So if you're using a delay to resynchronise the two signals, it's the DI that needs to be delayed, NOT the mic signal. And the necessary delay would be 1ms for each foot of distance between the guitar amp's speaker and the mic (or part thereof).

A better option, though, is to advance the mic signal in the DAW so that the timing of the original performance (captured instantly by the DI) is preserved. So drag the mic track earlier (to the left) to align it with the DI track. Since most people place the mic within about 6-inches of the guitar cab's speaker, expect to move the mic track only about 0.5ms or about 22 samples at a 44.1kHz sample rate -- but the correct alignment is usually quite obvious from the shape of the waveforms.

I understand that this is likely to be more important in the bass than it is the guitar...

No, again!

At low frequencies the phase shift between the DI and mic signals due to the miking distance is negligible. Consequently the DI and mic'd signals tend to reinforce each other constructively, rather than interfere destructively (which is more likely with the higher fundamentals of an electric geetar). So coluration is usually inaudible and time alignment unnecessary for a bass track.

H
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Re: How to split guitar signal?

Postby gingertimmins » Mon Sep 23, 2019 10:20 pm

Hugh Robjohns wrote:
gingertimmins wrote:I’ve read that due to the tiny time difference between mic’d signal and Di signal that I need to phase align the two.

You don't have to phase-align them...

If you choose to mix the DI signal and mic'd signal together (at similar levels) then the small timing difference between them may result in some comb-filtering colouration. But you may well like the effect, so I'd suggest having a listen first before dialling in the delay.

In one article it said to use a delay plug-in on the mic’d signal, set to around 2ms.

Er... No! :?

The DI signal is the direct electrical sound, arriving at (almost) the speed of light. The mic'd signal will be slightly late because of the much slower speed of sound through air -- the rule of thumb is 1ms per foot. So if you're using a delay to resynchronise the two signals, it's the DI that needs to be delayed, NOT the mic signal. And the necessary delay would be 1ms for each foot of distance between the guitar amp's speaker and the mic (or part thereof).

A better option, though, is to advance the mic signal in the DAW so that the timing of the original performance (captured instantly by the DI) is preserved. So drag the mic track earlier (to the left) to align it with the DI track. Since most people place the mic within about 6-inches of the guitar cab's speaker, expect to move the mic track only about 0.5ms or about 22 samples at a 44.1kHz sample rate -- but the correct alignment is usually quite obvious from the shape of the waveforms.

I understand that this is likely to be more important in the bass than it is the guitar...

No, again!

At low frequencies the phase shift between the DI and mic signals due to the miking distance is negligible. Consequently the DI and mic'd signals tend to reinforce each other constructively, rather than interfere destructively (which is more likely with the higher fundamentals of an electric geetar). So coluration is usually inaudible and time alignment unnecessary for a bass track.

H

You’re such a fountain of knowledge Hugh, thanks for the explanation!
Regarding delaying the mic/ Di signal , that was a typo on my part, I meant that I should delay the Di signal.
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Re: How to split guitar signal?

Postby James Perrett » Mon Sep 23, 2019 10:50 pm

One other suggestion - try flipping the polarity on one of the channels. Depending upon your signal chain, you may find that you prefer the sound with the polarity flipped.
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