Dual Sound Wave Generator can be perfectly in phase or can be shifted in frequency and phase relative to one another over the range of 0.1Hz to 40kHz. The waveform can be sine,triangle or sawtooth and waveforms can be added or one wave modulated by the other.
Dual Sound Wave Generator
Gelsonlab HSPW-021 Dual Sound Wave Generator for Educational teaching
A full entry keyboard permits the entry of any frequency or a shift of phase in degrees between the two signals.