Can a Shure SM7B plug straight into a PC?
No, and not because of gain. The SM7B has no converter inside it, so there is nothing on its XLR pins a USB port or a pink 3.5 mm jack could read. What the adapter cables really are is explained below.
Signal Chain Compatibility Matrix
Select gear and parameters for live gain, impedance and SPL calculations.
Input Equipment Setup
PASS: Optimal Signal Chain
Requires minimum +60dB of clean pre-amp gain. Most budget entry interfaces max out at +50dB to +56dB and introduce hiss at max pot. An inline preamp booster (Cloudlifter CL-1 / FetHead) is strongly recommended.
The interface preamp provides sufficient headroom.
$538
$405
-25%Tonal & acoustic characteristics: Flat, wide-range frequency response for clean music and speech. Smooth, warm acoustic character with air-suspension shock isolation.
Technical advisory: With +69dB max gain, the Gen 4 Solo can drive demanding dynamics like the Shure SM7B natively without requiring an external inline booster.
Physical Interconnect Topology
Shure SM7B
Direct Cable Connection (No Intermediate Box)
1x Shielded Balanced XLR Cable (3-Pin XLR Male to XLR Female)
Focusrite Scarlett Solo (Gen 4)
Host: Apple MacBook Pro (M1/M2/M3/M4)
Short answer: no. Not with an adapter, not with a converter cable that costs eight dollars, not at all.
The SM7B is an XLR-only dynamic microphone with no built-in analogue-to-digital converter. What leaves its three pins is a balanced analogue voltage of roughly −65.8 dBu at speaking level — millivolts. A USB port carries digital data; there is no arrangement of copper that turns one into the other. This is a topology mismatch, not a gain deficit, and the calculator on this page reports it as such: no amount of software or gain solves a missing converter.
What you need is a preamp and a converter, in one box or two. That is precisely what an audio interface is. For the SM7B specifically, look for one that publishes at least 60 dB of gain, or budget for a +25 dB inline booster in front of a smaller one.
The two traps. The passive "XLR female to 3.5 mm" adapters sold as microphone adapters are the worse one. A computer's pink jack is designed for an electret headset capsule and puts a small DC bias on the ring to power it; the SM7B ignores that bias, and its output sits far below what that input expects. You will get a faint, hissy, unbalanced signal and conclude the microphone is broken.
The second trap is subtler: XLR-to-USB cables — the Shure X2u and its relatives — do work, because they are a complete interface hidden in a barrel. But that barrel contains a preamp, and its gain range is the same question this page opened with. Before buying one for an SM7B, find the number.