At ultrasonic frequencies the reactance of the 4.7nF pre-emphasis capacitor is a dead short so the gain is 1+ (10k/1.5k)= 7.7 times (about 17dB).
When the reactance of the 4.7nF capacitor equals the resistor value of 1.5k ohms then the gain is reduced 3dB with a slope of 6dB per octave below it. At lower frequencies the gain is reduced until it is 1 where it stops decreasing. So the cutoff frequency is 1 divided by (pi x 4.7nF x 1.5k ohms)= 22.7kHz where the gain is -3dB at 14dB, and at 11.35kHz the gain is about 11dB, and at 5.7kHz the gain is about 5dB, and at about 2.9kHz the gain is 1.
EDIT again. Another way of calculating the pre-emphasis of the 4.7nF capacitor in series with the 1.5k resistor and when the opamp has a 10k negative feedback resistor is that the low frequency gain is 1 when the reactance of the capacitor is high, then when the reactance of the capacitor equals the value of the feedback resistor (10k) the gain is increased to 3dB and increases at 6dB per octave above until the reactance equals the 1.5k resistor when the gain is 3db from maximum gain of about 17dB.