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Why do audio interfaces have so little headroom in intrument (High Z) inputs?

LuckyDinosaur

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I just bought a Solid State Logic SSL2 MKII and in every other aspect I'm quite happy with it, but I've noticed this is a problem with most (all?) audio interfaces. Even if you are using medium output passive humbuckers in your guitar, you need to have the gain at zero or almost zero in order to avoid the input indicators going red. Some people would suggest "just lower your guitar volume", the problem is that with passive guitars lowering the volume also changes the tone, using the volume at max is quite common and part of the sound of most guitarrists.
I've seen people complaining of this bad design for decades and one would imagine the enginers working for pro and prosumer audio companies would do better than this for such a basic aspect. Do they even plug an electric guitar when testing their designs? Aren´t they aware people have been complaining about it for years? I don´t get it. :(
Something interesting is that one of the reasons I bought the SSL2 MKII was because it had the highest maximum input of my other options, the specs state "Max Instrument Input Level: +15 dBu", wouldn´t that be equal to 4.3V? On paper sounds like plenty, but in the practice it´s not. Maybe I'm missing something.
 
It is quite common for input level indicators turning red way below actual clipping, like 6dB or even more, to warn the user that the signal is fairly hot.
Like @AnalogSteph said, one should check the waveform of the recording to see if it is actually clipped or not. Also, the better interfaces should show soft-clipping which doesn't not damage the signal peaks too much in case of actual moderate overload.

4.3Vrms (6.1Vpk) should really be OK for almost anything. At my day job I'm currently designing an interface which can run 4Vrms undistorted and has another 3dB of analog soft-clipping on top of that, and the actual analog-to-digital converter is never clipped even with the most severe overdrive.

Electric bass is often more problematic with regard to peak levels than guitar but sustained levels above 4Vrms -- where even soft-clipping would be really annoyingly apparent -- are rare IME (except for active basses with EQ, some of them running off of two 9V block, for a reason).
 
I agree lowering the volume control of a passive circuit is not ideal at all. Have you looked at the waveform to confirm it's clipped? Is your guitar a stock build?
 
I know this used to be a fairly common complaint with the 1st-gen Scarletts, but hardly ever since then. You can keep matters out of clipping with the gain at minimum though, right? What are the actual digital peak levels you are seeing in your DAW then?
Yes, the good thing is that as you say, I can get away by setting the gain at minimum with all my guitars and basses, except for one of my guitars that has a really hot bridge pickup (Dimarzio X2N), but only in very specific notes if I play really hard with palm muting. Anyway, I think it would be good to have more room for adjustability.
I agree lowering the volume control of a passive circuit is not ideal at all. Have you looked at the waveform to confirm it's clipped? Is your guitar a stock build?
Electric bass is often more problematic with regard to peak levels than guitar but sustained levels above 4Vrms -- where even soft-clipping would be really annoyingly apparent -- are rare IME (except for active basses with EQ, some of them running off of two 9V block, for a reason).
I have a lot of guitars and a couple basses with a variety of pickups ranging from low to very high output. I play mostly metal and I'm used to hit the strings really hard whem playing heavy riffs ("chug-chug-chug" haha), so I gues that´s part of my problem. With vintage style single coils an my passive bass I can go ass high as 10 or 11'o clock with the gain, with medium output humbuckers and muy active bass (if I dont boost frequencies) I can go as high as 9'o clock, with high output humbuckers like Duncan Distortion or active bass if I boost frequencies I can go as high as 8'o clock and lastly, with my guitar that has a DiMarzio X2N I must have the gain at minimum and trying not to get too excited while playing. I guess with that last one I'm gonna need to lower the pickup a little or to use a DI Box with a pad just to be on the safe side. Good thing I don´t like active pickups in my guitars.
At my day job I'm currently designing an interface which can run 4Vrms undistorted and has another 3dB of analog soft-clipping on top of that, and the actual analog-to-digital converter is never clipped even with the most severe overdrive.
That sounds great and pretty interesting. I would like to ask what interfase is that, but I gues you are working under a non-disclosure agreement.
 
As many of you probably know, we recorded all guitars direct at Motown using home made gear. After I moved to San Francisco in 1972, I was shocked to find that nearly everything available for recording direct guitars didn't have enough headroom. Manufacturers seem to just ignorantly copy each other to this day.
 
I have a lot of guitars and a couple basses with a variety of pickups ranging from low to very high output. I play mostly metal and I'm used to hit the strings really hard whem playing heavy riffs ("chug-chug-chug" haha), so I gues that´s part of my problem. With vintage style single coils an my passive bass I can go ass high as 10 or 11'o clock with the gain, with medium output humbuckers and muy active bass (if I dont boost frequencies) I can go as high as 9'o clock, with high output humbuckers like Duncan Distortion or active bass if I boost frequencies I can go as high as 8'o clock and lastly, with my guitar that has a DiMarzio X2N I must have the gain at minimum and trying not to get too excited while playing. I guess with that last one I'm gonna need to lower the pickup a little or to use a DI Box with a pad just to be on the safe side. Good thing I don´t like active pickups in my guitars.
My personal worst-case test is when you palm-slap all four string of a G&L bass with their big MFD-humbuckers in series config, that peaks at over 10 Volts easily. I tend to do this at times, to assist the drummer with a second kick drum, sort of. In that case, though, the clipped attack is actually helpful to create the clicky initial sound of a kick drum ;-)

As for guitars, my highest output comes from a neodymium humbucker (Entwistle Dark Star) when playing those chugg-chugg palm mutes, pounding in heavy. Then again, as this is a style I only use with distortion sound it doesn't matter much if the attack is clipped.

Where it really matters is playing jazz style with rolled-off treble and clean sound setting where any hard-clipping is completely unbearable and will totally spoil a recording.
Again using the Dark Star PU (in a semi-electric) I've found that 4Vrms clean headroom and gentle soft clipping above does the trick.
That sounds great and pretty interesting. I would like to ask what interfase is that, but I gues you are working under a non-disclosure agreement.
Well, yes, but what I can say is the ADC/DAC section is part of a bigger and complex DSP project with expanded analog and digital connectivity, to cover many different potential use cases, for musicians or music producers.
 
My personal worst-case test is when you palm-slap all four string of a G&L bass with their big MFD-humbuckers in series config, that peaks at over 10 Volts easily.
:eek: Whoa. That's not happening on any interface with a +/- 5 V supply then.

Hmm. Aren't a lot of pedals running on 9 V? How does that work out?

Not sure what the least expensive interface with a +/-12 V supply would be - Behringer UMC1820 perhaps? That can supposedly take +18 dBu on the instrument inputs. Supplies must be similarly high for the SSL 12 but it can still take only +14 dBu. Likewise, the circuitry in old Audients like the iD22 has relatively high distortion.
 
:eek: Whoa. That's not happening on any interface with a +/- 5 V supply then.

Hmm. Aren't a lot of pedals running on 9 V? How does that work out?
I have to add that these peaks can only be realised when the internal buffer / HF-boost preamp in the G&L bass is removed. Like pedals, it runs from 9V and cannot handle the peaks and it is useless for me anyway. While you can switch it off, the input remains connected to the pickup(s) and thus the circuit is back-powered by them (and still clipping the signal because of that ;-)

I don't play any pedals (except for a tuner with true relay bypass) so can't comment much.

Not sure what the least expensive interface with a +/-12 V supply would be - Behringer UMC1820 perhaps? That can supposedly take +18 dBu on the instrument inputs. Supplies must be similarly high for the SSL 12 but it can still take only +14 dBu.
It all depends on the first buffer amp in front of any volume control pot. It has to handle the voltage. In our design it's a rail-to-rail input/ouput opamp running on +-17V rails, and it's a balanced high-Z input and thus can handle over 30V peak values with a balanced source (which are then cropped down by the fast softclipper).
 
You can always reduce gain up front and then add it back on the way out. Not ideal but there are a lot of clean boosts out there that would make up 10dB if you had to trim the input down 10dB.

I even tested my outboard hi-Z input to confirm it'd have enough headroom for what the Internet said was a typical peak signal level and find it's clipping sometimes. Less so with an EMG 81 than the DiMarzio fortitude in my other guitar.

The Internet said to expect 500mV tops... But I'm getting several volts on percussive palm mutes.. signal level is the same when I run through my littlelab redeye except it doesnt clip, so I assume the transformer is just shaving off the peaks and I never realized it before
 
I use a Rupert Neve DI box for my guitar recordings, it works great and I have never had any problems with clipping.
 
Not sure it’s been shared before. This interface, as several others, uses a combo XLR/Jack inputs. When connecting an XLR cable, it assumes you connected a microphone, and goes high gain.
When connecting an instrument or line level device, only use a TRS/TS connector (jack).
With a guitar, it’s necessary to press the two buttons “Line” and “Hi-Z” because it’s high impedance source.
 
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