Question about using a mic pre through an interface pre

[Kirkl]

Hi,

I've read quite a number of threads here on Gearslutz looking for an answer to this question. I apologize if it's here somewhere, but I couldn't find it.

Preamble:

A lot of threads recommend using high quality mic pre's instead of the pre's that come with your audio interface. I have, for example, a new FireFace 400 and I understand that it's pre's are not too bad. When I put a hardware mic pre in front of my FF400 the signal still goes through the pre that comes with the interface, albeit at a higher amplitude requiring less work on the part of the FF400 pre. So...

Question(s):

What is my motivation for putting a hardware mic pre in front? Is it to prevent any distortion or colouring that the "lesser" pre's in my FF400 are introducing by requiring less work of them (BTW, I don't hear any distortion or colouring from the FF pre's - they sound clean and neutral to me) or is it to colour the sound in a pleasing way? If it's to colour the sound, then why wouldn't I do that later, after I've recorded it? That would give me a lot more control, wouldn't it? I could try a huge number of ways to colour it, including looping it through any number of mic pre's until i get the sound I like best.

Thanks in advance for your help and for your patience with a neophyte.

[doulos24]

you don't go into the front mic preamps that would add unneeded noise you use the line ins inputs 5-8 of the interface bypassing the preamps all together

[hossman777]

My Tascam US1641 doesn't have enough line-ins for me to hook up all my external preamps. So, I have 4 going into the mic pres on the US1641 with the gain on the US1641 dumped all the way down. I don't have any trouble doing it that way. I know it's not "proper" but it is functional and I'm working within my current limitations, so "proper" for me right now is whatever I can make work without screwing sound quality. Sending my Ramsa console pre's through the pres 1-4 on my Tascam interface with the gain dumped all the way down introduces no detectable extra noise, and it doesn't screw my sound quality.

Short answer: Yes you can, if you must. Not ideal, but it can be made to work.

[Kirkl]

Gotcha! Thanks. Inputs 5 to 8 don't go through the preamps! Makes sense. Wasn't obvious to me from reading the RME manual, but upon re-reading with your input I see that the preamps are not mentioned in the section about the Line Rear inputs, while they are in the Microphone input section.

[mhs2xs]

Originally Posted by hossman777

My Tascam US1641 doesn't have enough line-ins for me to hook up all my external preamps. So, I have 4 going into the mic pres on the US1641 with the gain on the US1641 dumped all the way down. I don't have any trouble doing it that way. I know it's not "proper" but it is functional and I'm working within my current limitations, so "proper" for me right now is whatever I can make work without screwing sound quality. Sending my Ramsa console pre's through the pres 1-4 on my Tascam interface with the gain dumped all the way down introduces no detectable extra noise, and it doesn't screw my sound quality.

Short answer: Yes you can, if you must. Not ideal, but it can be made to work.

I do the same thing w/ my Alesis Multimix w/ my Mackies upstream. Between the two, it's surprisingly quiet.

[Kirkl]

So...

I've got a UA Solo 610 mic pre. I bought it to add some tube colour when I want it. I guess that I need at least one more mic pre then, one that is more transparent. (I'll never be recording more than one thing at a time - guitar, voice or sax.) I have to say, however, that the FireFace 400 pre's sound pretty good to me. Maybe one of the local shops will let me buy another pre to try with the understanding that, if I don't hear a real difference, I can return it.

Thanks again.

[CrankyChris]

Question:

What if the mic input, balanced and hi - z input are all the same like this. There is no dedicated line input. So even if turned all the way down, I'm assuming it's not truly off.

I've often wondered (out loud in another thread) if external pre's in this situation is worth it. :shrug:

Anyone really know about the inner workings and how the sound is affected ?

[Bill@WelcomeHome]

cheap devices will often pad down the line input and still run it through the same mic pre circuit to boost the signal again. Saves them money. You get what you pay for.

[CrankyChris]

Originally Posted by Bill@WelcomeHome

cheap devices will often pad down the line input and still run it through the same mic pre circuit to boost the signal again. Saves them money. You get what you pay for.

Do you know of a unit whose balanced inputs bypass the micpre circuitry?

To me it looks like virtually every interface is a cheap-o. Cost seems to simply be a matter of # ins and outs.

[Nelson89]

Originally Posted by CrankyChris

Do you know of a unit whose balanced inputs bypass the micpre circuitry?

To me it looks like virtually every interface is a cheap-o. Cost seems to simply be a matter of # ins and outs.

M audio Profire 2626 bypasses the mic pre's entirely on its +4 line inputs....you can turn the knobs as much as you want, but they won't make a difference...These are actually in combo XLR/TRS inputs as well...except the hi-z input is kept separate. Only the XLR feed is sent through the preamp.

This isn't really an expensive interface either in the grand scheme of things...

I think you'll find there's quite a lot of interfaces out there that exhibit this behaviour...to say that virtually every interface doesn't do this just tells me you haven't done your research very well if at all...

[CrankyChris]

Originally Posted by Nelson89

M audio Profire 2626 bypasses the mic pre's entirely on its +4 line inputs....you can turn the knobs as much as you want, but they won't make a difference...These are actually in combo XLR/TRS inputs as well...except the hi-z input is kept separate. Only the XLR feed is sent through the preamp.

This isn't really an expensive interface either in the grand scheme of things...

I think you'll find there's quite a lot of interfaces out there that exhibit this behaviour...to say that virtually every interface doesn't do this just tells me you haven't done your research very well if at all...

What is the magic phrase I should look for that guarantees the mic pre circutry is bypassed?

[Bill@WelcomeHome]

Originally Posted by Nelson89

M audio Profire 2626 bypasses the mic pre's entirely on its +4 line inputs....you can turn the knobs as much as you want, but they won't make a difference...These are actually in combo XLR/TRS inputs as well...except the hi-z input is kept separate. Only the XLR feed is sent through the preamp.

...

You know this from looking at the circuit? That is the only way to tell, short of the manufacturer saying so.

[Nelson89]

Originally Posted by CrankyChris

What is the magic phrase I should look for that guarantees the mic pre circutry is bypassed?

It's not so much looking for a phrase i don't think, its more about knowing how to read the specs properly, circuit diagrams too. If the line input has adjustable trim...its not bypassing anything, if it doesn't, generally its bypassing.

Another one i've noticed is that if its an unbalanced -10 input, generally it's still going through the pre...

To give an example, this is in the spec sheet for the m audio profire 2626:

Line Inputs (Balanced)

Frequency Response +/- 0.1dB, 20Hz to 22kHz (48kHz)
+/- 0.4dB, 20Hz to 80kHz (192kHz)

Dynamic Range 110dB, A-weighted

Signal-to-Noise Ratio -110dB, A-weighted

THD+N 0.0008% (-102dB), 1kHz, -1dBFS

Crosstalk -120dB @ 1 kHz

Maximum Input level +19.6dBu, typical

Input Impedance >20k Ohms, balanced

You'll notice there's no "gain range" or "variable trim"...in this case, its completely bypassing the mic pre.

On the other hand, this is from the Presonus Firestudio:

Line Inputs (1/4” TRS, Channels 3-8)
Frequency Response (+0, -5 dB).....20 Hz to 50 kHz
Frequency Response (+0/-3.0 dB).....20 Hz to 150 kHz
Input Impedance..... 10 kΩ
THD + N (unwtd, 1 kHz @ +4 dBu Output, Unity Gain)..... < 0.003%
S/N Ratio (Unity Gain, unwtd, Ref = +4 dBu, 20 Hz to 22 kHz)..>101 dB
Gain Control Range (+/- 1 dB) ..... -9 dB to +12 dB
Maximum Input level (Unity Gain, 1 kHz @ 0.5% THD+N).....+23dBu

Hopefully that came out semi readable, but as you can see in this case, the firestudio doesn't bypass the pre's

Its just about being able to interpret the spec's properly...of course sometimes the spec's are wrong, but the only way to know that is to physically test the unit yourself.

[Bill@WelcomeHome]

Originally Posted by CrankyChris

Do you know of a unit whose balanced inputs bypass the micpre circuitry?

To me it looks like virtually every interface is a cheap-o. Cost seems to simply be a matter of # ins and outs.

Sorry Chris, I can't help you there. I have had separate mic pres and converters for longer than most currently popular combo interfaces have been in existence.

But the same thing is true with inexpensive consoles. It is just a matter of money, to pad an input is cheaper than to provide a separate mic pre and a line pre for each channel. With everyone wanting every feature on the planet for $1.99.... but there is a reason why more expensive gear costs more, it is not just a plot or agreement between studios and manufacturers to keep costs high and exclude the budget-minded from making good recordings.

I'm not saying that it won't make a difference in the sound. I happen to believe that the devil is in the details and even the component quality has an effect on the sound. But on balance, is this the biggest problem in your room? Or are there other issues which will affect the over-all sound more profoundly? I do not think that I would worry a great deal about this particular issue until i was ready to step up significantly in quality. Once you start to separate the components, which makes it more expensive on one hand but on the other makes it easier to upgrade quality without having to change -everything- , that will bypass this issue entirely.

[nathanp]

Running an external pre through an interface pre certainly isn't optimal. But I don't think it's really as bad of a thing as some people would have you believe. If you don't turn up the gain on your interface's pre, your not going to get much extra noise. As to whether or not it affects the sound of the external pre when it's set at that low of a level, I don't know.

I have done this with my focusrite saffire pro 40, and as long as I don't turn the gain on the focusrite up to the point where it would normally make noise (I usually keep it much lower than that), there's no noticeable noise addition or coloration. The pres in the saffire series (as well as in the octopre preamps) are acclaimed for being extremely low noise and transparent. Only problem is they only have like 50 db gain or something... So running an external pre through them really does not degrade the sound of the external in any way. I used to use my external pres through a device that had line ins that bypassed the internal pres and they don't sound any different now than they did back then.

Maybe on units with cruddier built in pres than the focusrites, it would be different? I don't know.

$0.02