Not good
First it was good app, but now it is not… Why we should pay a subscription for a sound like pi-pi-pi. Really? Devices can not produce that low frequency sound because of its limitations. You need professional equipment to do that but it is not cheap and sometimes illegal. I have measured the wave, nothing low frequency sound. If we need 20Hz yes possibly, but sometimes it is 25Hz not 20Hz. You need a subwoofer to produce that sound.