Electronic channel sounding plays a vital role in developing wireless communication systems. It is critical for transceivers' equalization and filtering operations. However, current pure electronic channel sounding techniques are not well-suited for emerging scenarios such as opportunistic spectrum access, channel impulse response (CIR) based wireless positioning, and wireless security applications, which demand rapid, high-resolution, and spectrum agile channel measurements on commercial off-the-shelf (COTS) devices. To address these critical issues, this paper proposes EV-Sounding, a novel methodology for visual assisted electronic channel sounding. Based on frequency domain channel sounding, EV-Sounding leverages cameras for visual estimation of sparsity locations to reduce the number of frequency samples, thus speeding up the sounding process. EV-Sounding achieves both high-resolution CIR measurements and spectrum agility. We prototype an EV-Sounding system on COTS devices. Our real-world experimental results and extensive simulations validate EV-Sounding's performance.