What happens when you use an Audio Interface with an AMP

[kristinawilllove]

Hey all,

I currently have a pair of XENNS Mangrid Tops and a Schiit Magni Unity (with DAC). Definitely overkill but they're so good. However, I am unable to use a Mic with this configuration, hence I am looking for an Audio Interface.

I realised I could still use my Magni Unity if I connect the line out from an audio interface into the line in on my Magni Unity, and then switch to line mode. This will allow me to keep my IEMs plugged into my DAC/AMP and then I can use the USB switch if I just want to listen to things, and then use the line switch if I want to use my microphone.

I have a few questions regarding how the audio interface works with this setup. Will there be noise added, latency, higher volume? Given that I am using a pair of IEMs with a low impedance of around 20 ohms I heard that a lot of audio interfaces can struggle with them if you plug them straight in, so I was wondering if using my setup would counteract this or still have the same issue? Additionally, the main reason I want to use an audio interface for this in the first place is that I want direct monitoring of my incoming mic to my IEMs so I can hear myself. So I was wondering if this also might cause issues or not, given there might be a small bit of latency added.

I think thats enough questions for now, I could talk about what kind of Audio Interface I am looking for but I feel like its important to get some answers to the above questions before I ask for suggestions.

Thanks for the help in advance!

 

[Vincent Kars]

Given that I am using a pair of IEMs with a low impedance of around 20 ohms I heard that a lot of audio interfaces can struggle with them if you plug them straight in

They don't struggle but often the headphone out has a relative high impedance. Hence you have insufficient damping. Rule of the thumb is that the impedance of the headphone should be minimal 8 times the impedance of the headphone amp.
Often het headphone out is a bit down on power. If this is a problem, you might use a dedicated headphone amp connected to the line out.
Just an example: https://www.audiosciencereview.com/...rlett-2i2-audio-interface-gen-3-review.10187/

 

[AnalogSteph]

I realised I could still use my Magni Unity if I connect the line out from an audio interface into the line in on my Magni Unity, and then switch to line mode.

I generally recommend making use of the audio interface's headphone output instead, which saves you some hassle with correctly adapting balanced outputs. A 3.5 mm or 1/4" (6.3 mm) output is guaranteed unbalanced and adapter cables to RCA are readily available.

Will there be noise added, latency, higher volume?

a) only if your volume / gain settings are silly (you should have a tremendous amount of flexibility like this)
b) basically none at all (it's an analog amp and some cable, how much group delay could there possibly be? definitely <<1 ms)
c) if you set amplifier gain accordingly...

 

[kristinawilllove]

They don't struggle but often the headphone out has a relative high impedance. Hence you have insufficient damping. Rule of the thumb is that the impedance of the headphone should be minimal 8 times the impedance of the headphone amp.
Often het headphone out is a bit down on power. If this is a problem, you might use a dedicated headphone amp connected to the line out.
Just an example: https://www.audiosciencereview.com/...rlett-2i2-audio-interface-gen-3-review.10187/

Ok so for example the new Focusrite Gen4 Audio interfaces are a no go because they have an impedance of 50 ohms where as my IEMs have a low impedance of 20 ohms. So I'm looking more for something like the MOTU M2 which has an impedance of less than 1.

As I was talking about before, if I just routed the audio straight out of the interface to my Magni Unity, would this be an issue?

 

[kristinawilllove]

I generally recommend making use of the audio interface's headphone output instead, which saves you some hassle with correctly adapting balanced outputs. A 3.5 mm or 1/4" (6.3 mm) output is guaranteed unbalanced and adapter cables to RCA are readily available.

a) only if your volume / gain settings are silly (you should have a tremendous amount of flexibility like this)
b) basically none at all (it's an analog amp and some cable, how much group delay could there possibly be? definitely <<1 ms)
c) if you set amplifier gain accordingly...

I don't really understand what I would need to adapt here? I already have my IEMs connected to my Magni Unity, and all I need to do is connect the line out from the audio interface to the line in of the Magni using some RCA cables.

How does the volume work when connected like this? Lets say when I have the Unity connected by itself it can go to 1-10. And then audio interface can go from 1-6. If I connect these together can it go from 1-16? Or is both volumes halved? Or is it a bit of a mix and match?

 

[Vincent Kars]

As I was talking about before, if I just routed the audio straight out of the interface to my Magni Unity, would this be an issue?

Of course not.

 

[kristinawilllove]

Thanks for the clarification.

Given everything we've talked about, would you recommend any good audio interfaces? I'm looking for something around £200 more or less. With preferably XLR inputs on the back of the device, I think it looks a lot better. I only really need one for a mic, nothing else. Additionally, it needs to have direct monitoring.
Besides that, I like a clean look, nothing too distracting. Honestly the less lights the better, so preferably an easy way to turn it off (software/button).

Are there any audio interfaces that have good software control? Maybe something I could use a remote or create shortcuts on my keyboard to do specific things like turning it on or changing the volume etc. Not really required, just curious of whats out there.

 

[Nutul]

I'd suggest you take a look at Julian Kreuse YT channel for an interface of your choice.
He tells every little bit of the devices he reviews, mic-input sensitivity, head/ear phone sensitivity / volume / performance, noise ratio, dynamic range, output volume, latency, and whatnot.
I believe a Focusrite Scarlett 3rd, or 4th gen. has everything you need; Julian also reviewed them both, so you can decide for yourself. The Motu M2 is another (IMO even better) option.

 

[kristinawilllove]

I'd suggest you take a look at Julian Kreuse YT channel for an interface of your choice.
He tells every little bit of the devices he reviews, mic-input sensitivity, head/ear phone sensitivity / volume / performance, noise ratio, dynamic range, output volume, latency, and whatnot.
I believe a Focusrite Scarlett 3rd, or 4th gen. has everything you need; Julian also reviewed them both, so you can decide for yourself. The Motu M2 is another (IMO even better) option.

Yeah he does some great videos. My issue with a lot of them is the XLR input being on the front of the device instead of the back. Looking more at some audio interfaces, the Audient Evo 4 looks great. It has a lot of features, I don't really care about my Mic sounding amazing, just decent is fine by me. But the mixing control between computer and mic audio seems like such a useful feature for my needs that a lot dont offer.

 

[AnalogSteph]

I don't really understand what I would need to adapt here? I already have my IEMs connected to my Magni Unity, and all I need to do is connect the line out from the audio interface to the line in of the Magni using some RCA cables.

A fair few audio interfaces don't even have RCA outputs though. The most common type is 1/4" TRS pairs with all kinds of balanced output implementations... which means that the correct pinout for an adapter cable is going to depend. (It's usually either RaneNote 110 #10B or #16A.) A TRS stereo headphone jack does not present such challenges, that's always L-R-GND and any garden variety adapter cable for this particular use case will work.

How does the volume work when connected like this? Lets say when I have the Unity connected by itself it can go to 1-10. And then audio interface can go from 1-6. If I connect these together can it go from 1-16? Or is both volumes halved? Or is it a bit of a mix and match?

These printed-on scales are entirely arbitrary and uncalibrated. ("These go to 11!" ) They are merely serving as a form of orientation to the user and are not quantitative in any way.

If you wanted to do it 100% correctly, the Magni Unity alone would need 3 sets of scales, one for each of its low, medium and high gain settings: -∞ to -10 dB, -∞ to 0 dB and -∞ to +15 dB. (For an average cheap pot, I would probably go from -∞ straight to 40 dB below max as the first real marking, as production tolerances down there can be very high. Arbitrary markings, by contrast, never have to be held to any kind of standard, and can be printed on willy-nilly = cheap.)

Even if we are going with just the middle version and are assuming that the user won't mind subtracting 10 or adding 15 as needed, negative numbers in the mysterious unit of dB (decibels) aren't what is being considered sexy to average consumers. Which is a huge bummer, as dBs make dealing with ratios of all kinds super easy once you've got the hang of it. You've got a signal chain with a volume pot turned down to providing 50 dB of attenuation followed by an amplifier with 15 dB of gain? That's 15 dB - 50 dB = -35 dB of gain or 35 dB of attenuation in total right there. Sure beats having to multiply 0.00316 and 5.62, doesn't it? Getting the hang of dBs is one of the most useful things to learn if you ever need to deal with signal levels of any kind.

(I wouldn't mind if "arbitrary positive scale" labels could just be ditched entirely. It would be an initial complication but make things so much more clear for users in the long run.)

If you run an audio interface headphone out into an external amplifier like the Magni Unity, it is going to apply its total overall gain to the signal. Audio interface output in turn can be measured, e.g. in Vrms at full tilt at a certain digital level in dBFS. If you then calibrate its volume knob, you can basically squash the entire audio chain together and determine overall gain e.g. in dBV / dBFS.

"How do I set these bloody knobs?" is officially known as a gain staging problem. Pro audio folks are confronted with those all the time, any basic mixer will pose one for starters. Here's a little intro:

Gain Staging: What It Is and How to Do It

Gain staging is tough to understand—so let us explain it! In this article, we’ll give you a modern approach to gain staging, as well as a brief history of the term in analog and digital contexts.

www.izotope.com

You can triangulate the matter by looking at some extremes:

If you turn up the audio interface to max, you may end up overdriving the amplifier's input (although I suspect it's one of those "volume pot first" deals that can take an absolute ton of level), or risk having to set its volume knob so low that you hit the pot's regions of poor channel balance. Some audio interfaces can even clip internally with a 0 dBFS signal at the high end, one user's bitter complaints about the Tascam UA-2x2HR come to mind. (I didn't quite get the fuss, I see it as a "then don't move you arm like that" kind of problem with some extra gain being available if you ever need it.)

By contrast, if you turn down the audio interface output a lot, its signal eventually will come too close to the inherent noise floor, and hiss will be heard once you have dialed in the amplifier gain for your desired listening volume, if that is being reached at all.

In practice, you can expect substantial leeway between these extremes. With today's tech, it may be 40-50 dB or even more still.

Oh, and maybe this is obvious, but output impedance is only critical wherever headphones are directly attached. Once you run a headphone output into a line-level input, the latter's input impedance is so high that 50 or 100 ohms of output impedance still is entirely negligible in comparison. In case of the Magni Unity that's 50 kOhms, largely resistive in nature, so very high with no variable impedance shenanigans to speak of.

 

[kristinawilllove]

A fair few audio interfaces don't even have RCA outputs though. The most common type is 1/4" TRS pairs with all kinds of balanced output implementations... which means that the correct pinout for an adapter cable is going to depend. (It's usually either RaneNote 110 #10B or #16A.) A TRS stereo headphone jack does not present such challenges, that's always L-R-GND and any garden variety adapter cable for this particular use case will work.

These printed-on scales are entirely arbitrary and uncalibrated. ("These go to 11!" ) They are merely serving as a form of orientation to the user and are not quantitative in any way.

If you wanted to do it 100% correctly, the Magni Unity alone would need 3 sets of scales, one for each of its low, medium and high gain settings: -∞ to -10 dB, -∞ to 0 dB and -∞ to +15 dB. (For an average cheap pot, I would probably go from -∞ straight to 40 dB below max as the first real marking, as production tolerances down there can be very high. Arbitrary markings, by contrast, never have to be held to any kind of standard, and can be printed on willy-nilly = cheap.)

Even if we are going with just the middle version and are assuming that the user won't mind subtracting 10 or adding 15 as needed, negative numbers in the mysterious unit of dB (decibels) aren't what is being considered sexy to average consumers. Which is a huge bummer, as dBs make dealing with ratios of all kinds super easy once you've got the hang of it. You've got a signal chain with a volume pot turned down to providing 50 dB of attenuation followed by an amplifier with 15 dB of gain? That's 15 dB - 50 dB = -35 dB of gain or 35 dB of attenuation in total right there. Sure beats having to multiply 0.00316 and 5.62, doesn't it? Getting the hang of dBs is one of the most useful things to learn if you ever need to deal with signal levels of any kind.

(I wouldn't mind if "arbitrary positive scale" labels could just be ditched entirely. It would be an initial complication but make things so much more clear for users in the long run.)

If you run an audio interface headphone out into an external amplifier like the Magni Unity, it is going to apply its total overall gain to the signal. Audio interface output in turn can be measured, e.g. in Vrms at full tilt at a certain digital level in dBFS. If you then calibrate its volume knob, you can basically squash the entire audio chain together and determine overall gain e.g. in dBV / dBFS.

"How do I set these bloody knobs?" is officially known as a gain staging problem. Pro audio folks are confronted with those all the time, any basic mixer will pose one for starters. Here's a little intro:

Gain Staging: What It Is and How to Do It

Gain staging is tough to understand—so let us explain it! In this article, we’ll give you a modern approach to gain staging, as well as a brief history of the term in analog and digital contexts.

www.izotope.com

You can triangulate the matter by looking at some extremes:

If you turn up the audio interface to max, you may end up overdriving the amplifier's input (although I suspect it's one of those "volume pot first" deals that can take an absolute ton of level), or risk having to set its volume knob so low that you hit the pot's regions of poor channel balance. Some audio interfaces can even clip internally with a 0 dBFS signal at the high end, one user's bitter complaints about the Tascam UA-2x2HR come to mind. (I didn't quite get the fuss, I see it as a "then don't move you arm like that" kind of problem with some extra gain being available if you ever need it.)

By contrast, if you turn down the audio interface output a lot, its signal eventually will come too close to the inherent noise floor, and hiss will be heard once you have dialed in the amplifier gain for your desired listening volume, if that is being reached at all.

In practice, you can expect substantial leeway between these extremes. With today's tech, it may be 40-50 dB or even more still.

Oh, and maybe this is obvious, but output impedance is only critical wherever headphones are directly attached. Once you run a headphone output into a line-level input, the latter's input impedance is so high that 50 or 100 ohms of output impedance still is entirely negligible in comparison. In case of the Magni Unity that's 50 kOhms, largely resistive in nature, so very high with no variable impedance shenanigans to speak of.

Thank you for the in depth overview of gain staging and making me aware of the potential issues etc. It might just be easier to get the Topping E2x2 and plug my IEMs straight into there, then I wouldn't have to deal with any extra cables and fiddling with knobs. It would be a shame to let my Unity go unused though, I did like the idea of just flicking the switch to use it over my audio interface when I wasnt using a mic.

I'm still a little confused with the cable side of things. How do you know if an audio interface takes a TS connection (for example using a cable like #16) over an audio interface that can only take a TRS cable (but using #10b). Lets take the Topping E2x2 for example, the specs on their website says the connector type is a 6.35mm TRS balanced jack: Tip (Hot), Ring (Cold), and Sleeve (Shield). What would be the appropriate cable in this case? Additionally, how do you know what your buying is correct? Do you have to try and get a custom cable made to fit your needs.

 

[Nutul]

How do you know if an audio interface takes a TS connection (for example using a cable like #16) over an audio interface that can only take a TRS cable

Usually all audio interfaces have balanced outputs and therefore use TRS (or XLR, but this makes things more clear since the beginning...)
Usually, again, they state the connector type and the signal geometry in their technical specifications. But then again, 99.99% of the audio interfaces, professional or consumer grade they be, the jacks are TRS, and not TS.

 

[kristinawilllove]

Usually all audio interfaces have balanced outputs and therefore use TRS (or XLR, but this makes things more clear since the beginning...)
Usually, again, they state the connector type and the signal geometry in their technical specifications. But then again, 99.99% of the audio interfaces, professional or consumer grade they be, the jacks are TRS, and not TS.

I thought you could still plug in a TS cable into the TRS jack and it would just treat it as unbalanced? Is this not the case? You need to specifically use a TRS cable that goes to RCA.

 

[Nutul]

I thought you could still plug in a TS cable into the TRS jack and it would just treat it as unbalanced? Is this not the case? You need to specifically use a TRS cable that goes to RCA.

Of course you have to; otherwise you'll end up shortening one of the signals (I think the negative one, but it's not this the point) that make up the differential output...
Anyway, making a suitable cable based on the interconnection diagrams pointed out above should be fairly easy if you can manage a soldering iron.

 

[kristinawilllove]

Of course you have to; otherwise you'll end up shortening one of the signals (I think the negative one, but it's not this the point) that make up the differential output...
Anyway, making a suitable cable based on the interconnection diagrams pointed out above should be fairly easy if you can manage a soldering iron.

Lets take the Topping E2x2 for example, the specs on their website says the connector type is a 6.35mm TRS balanced jack: Tip (Hot), Ring (Cold), and Sleeve (Shield). What would be the appropriate cable in this case?

Going back to this example then, which would be the correct cable from the diagrams pointed out in the previous post. Its either 10B or 16A just trying to understand when it is either of those? Or can you go with either.

 

[Nutul]

Going back to this example then, which would be the correct cable from the diagrams pointed out in the previous post. Its either 10B or 16A just trying to understand when it is either of those? Or can you go with either.

I understand you need to go from a TRS Jack to an RCA, so you may want a 10A. This will take the "hot" and the "shield" (signal GND), leaving the "cold" floating, that is: unused and safely away from signal ground...
Assuming your TRS outs are "standard" 4V, this will give you "standard" 2V on your RCA.

 

[retroflex]

I understand you need to go from a TRS Jack to an RCA, so you may want a 10A. This will take the "hot" and the "shield" (signal GND), leaving the "cold" floating, that is: unused and safely away from signal ground...
Assuming your TRS outs are "standard" 4V, this will give you "standard" 2V on your RCA.

What are you basing this on? (Specifically, the "cold [...] safely away from signal ground" part, implying that connecting cold to ground is a very stupid idea).

I used a TS<->RCA cable from my Focusrite interface yesterday and it was completely fine. TS plug into 6.3mm hole is the way things have worked for decades, if an audio interface doesn't handle cold being shorted to ground (EDIT: in a TRS connector) it's defective imho.

 

[Nutul]

if an audio interface doesn't handle cold being shorted to ground it's defective imho.

You may be a lucky guy. I never shorten anything to ground. The diagrams to correctly build those cables are there for a reason.
I suggest things out of my electronic knowledge, and common sense.

 

[kristinawilllove]

What are you basing this on? (Specifically, the "cold [...] safely away from signal ground" part, implying that connecting cold to ground is a very stupid idea).

I used a TS<->RCA cable from my Focusrite interface yesterday and it was completely fine. TS plug into 6.3mm hole is the way things have worked for decades, if an audio interface doesn't handle cold being shorted to ground it's defective imho.

Thanks for a second opinion, as I spoke to a custom cable company about this and they said the TS to RCA cable would be fine for my needs, so I was starting to question the companys word.

 

[retroflex]

You may be a lucky guy. I never shorten anything to ground. The diagrams to correctly build those cables are there for a reason.
I suggest things out of my electronic knowledge, and common sense.

I've edited my comment a little to clarify that I'm talking about TRS connectors here; shorting cold to ground on an XLR output is probably a bad idea if you don't know what the driving circuit looks like. However, it is a fact that audio pros will connect anything to anything that fits, so any studio equipment with 6.3mm jacks that don't handle TS connectors will probably be very short lived, and will garner a ton of negative reviews. So I don't feel lucky, I feel rather comfortable.