Topping E1X2 OTG Interface - Mic gain/DAC Quality - Opinions Needed

[Finale]

Hi there,

Recently picked up a Topping E1X2 OTG interface and noticed a couple of things I’d love some input on:

1. Mic gain: It claims to have 58dB of gain, but with my XM8500 mic (which is a relatively sensitive dynamic mic), I need to crank the mic gain knob almost to 100% to get comfortable listening levels (-12). Based on Julian Krause's review this interface has HF roll off past 80% gain. or else I’m forced to use digital gain, which concerns me as it might impact audio quality.. Is this normal? I can't imagine pairing power hungry mics like sm7b with this.

2. DAC quality: From my untrained ears the internal DAC output seems audibly worse compared to another DAC (khadas Tone board/ES9028QM chip) I’ve been using. Has anyone else experienced this? or Is it just expected from an audio interface vs dedicated DAC? It is a bit disappointing as I purchased this hoping to consolidate mic amp, DAC, and headphone amp into a single device.

Would appreciate any thoughts or advice!

 

[AnalogSteph]

1. Mic gain: It claims to have 58dB of gain, but with my XM8500 mic (which is a relatively sensitive dynamic mic), I need to crank the mic gain knob almost to 100% to get comfortable listening levels (-12). Based on Julian Krause's review this interface has HF roll off past 80% gain. or else I’m forced to use digital gain, which concerns me as it might impact audio quality.. Is this normal? I can't imagine pairing power hungry mics like sm7b with this.

Ah, the old chestnut about digital gain... All you really need is for analog preamp noise to trounce ADC noise by at least 10, preferably closer to 20 dB, assuming its gain still is high enough for preamp EIN to remain near its optimum. Since ADC dynamic range is quite substantial at 118 dB(A), that takes less gain than you might think. Max input with a 150 ohm mic is +8.6 dBu, -118 dB(A) = -109.4 dBu(A), vs. a nominal EIN of -130.5 dBu(A), so you'd want a tad over 30 dB minimum, and ideally more like 40 dB. That's close to 20 dB short of maximum. At that point you can easily enable the optional +20 dB digital gain to make up for any shortfall in monitoring levels.

Now with a 600 ohm mic like the XM8500, its thermal noise alone will be about -124.9 dBu unwtd, so you can't really hope for less than -127.2 dBu(A), though the 1.5 kOhm input impedance means you lose about 2.1 dB of level over a 150 ohm mic of same sensitivity (e.g. SM58), so let's say -129.3 dBu(A). That's already over a dB higher before even considering preamp noise, so you can actually expect things to be a bit less critical than estimated above.

BTW, in the interest of levels I hope that your mic to mouth distance isn't an awful lot greater than about 2 inches (5 cm), which is what vocal mics tend to be optimized for in terms of response. Getting rid of plosives may involve placing the mic quite substantially off-axis, so don't be too surprised if it ends up at 45-60° or something.

 

[Finale]

Ah, the old chestnut about digital gain... All you really need is for analog preamp noise to trounce ADC noise by at least 10, preferably closer to 20 dB, assuming its gain still is high enough for preamp EIN to remain near its optimum. Since ADC dynamic range is quite substantial at 118 dB(A), that takes less gain than you might think. Max input with a 150 ohm mic is +8.6 dBu, -118 dB(A) = -109.4 dBu(A), vs. a nominal EIN of -130.5 dBu(A), so you'd want a tad over 30 dB minimum, and ideally more like 40 dB. That's close to 20 dB short of maximum. At that point you can easily enable the optional +20 dB digital gain to make up for any shortfall in monitoring levels.

Now with a 600 ohm mic like the XM8500, its thermal noise alone will be about -124.9 dBu unwtd, so you can't really hope for less than -127.2 dBu(A), though the 1.5 kOhm input impedance means you lose about 2.1 dB of level over a 150 ohm mic of same sensitivity (e.g. SM58), so let's say -129.3 dBu(A). That's already over a dB higher before even considering preamp noise, so you can actually expect things to be a bit less critical than estimated above.

BTW, in the interest of levels I hope that your mic to mouth distance isn't an awful lot greater than about 2 inches (5 cm), which is what vocal mics tend to be optimized for in terms of response. Getting rid of plosives may involve placing the mic quite substantially off-axis, so don't be too surprised if it ends up at 45-60° or something.

Thanks for your kind reply! As a casual DAC user, I’ll admit some of the technical terms and equations went a bit over my head, lol. By the way, the XM8500 actually has an impedance of 150 ohms, not 600 ohms. I usually keep the mic at a distance of about 2–3 inches, any closer would result in a pretty noticeable proximity effect.

 

[AnalogSteph]

By the way, the XM8500 actually has an impedance of 150 ohms, not 600 ohms.

I'm not sure I would trust the specs in that regard, they're a bit... sus. 99% of cheap dynamic mics use a 600 ohm capsule, as it means you can get away with larger tolerances while still delivering decent output level. If in doubt, ask a multimeter.

I usually keep the mic at a distance of about 2–3 inches, any closer would result in a pretty noticeable proximity effect.

I mean, it's not like there is no proximity effect even at that distance. Vocal mics tend to figure that into their tuning from the outset. You'll notice that a recording taken at arm's length sounds relatively thin even after compensating for the level difference. It also means that you can pretty much season their low end to taste by varying the distance.

This is also part of why typical dynamic mics tend to deliver dull and unexciting ambient recordings. There is not a lot of low end at long range, and the treble rolls off relatively early and the typical 1" capsule makes them quite directional up there, plus there usually are low/mid-treble peaks to aid intelligibility so things are quite uneven. Not to mention that noise levels are never truly great. This field tends to be the domain of pencil condensers and other small to medium diaphragm condenser mics.