It is a well-established fact that placing seismic instruments below the surface of the Earth will lead to improvements in the signal-to-noise ratio (SNR) at any given site. This is so for two basic reasons, both related to the fact that the uppermost layers of the Earth are typically very highly attenuative and low velocity. To better understand the depth dependence of improvements in signal-to-noise ratio for borehole seismic data, the authors collected and analyzed a data set recorded from a pair of high-fidelity, broadband (1 to 80 Hz) seismometers sited in two closely separated deep boreholes near Amarillo, Texas. The total decrease (surface to 1951 m) in minimum noise level is up to 30 dB; the total decrease in maximum noise level is up to 35 dB; and the range of noise values (maximum to minimum) at a given depth decreases from 30 to 10 dB. The majority of the noise reduction occurs within the first few hundred meters below the surface.