Here are two mathematical examples describing the cause and effect relationships:
1) If frequency is doubled from 100 Hz to 200 Hz while wavelength is held at 1 m, then wave speed will double from 100 m/s to 200 m/s.
2) If frequency is doubled from 100 Hz to 200 Hz while wave speed is held at 100 m/s, then wavelength will be halved from 1 m to 0.5 m.