The 639 Hz frequency is another one of the Solfeggio frequencies, often associated with various spiritual and healing properties. It is sometimes referred to as the "FA" frequency, based on the historical solmization (solfège) system. This frequency is believed to be related to harmonious relationships, emotional healing, and the reconnection of individuals with their inner selves and with others.
Just like other Solfeggio frequencies, it's essential to be aware that the healing and spiritual properties attributed to them are not scientifically proven. These frequencies have gained popularity in New Age and alternative medicine communities. People who use Solfeggio frequencies often do so in meditation, sound therapy, or relaxation practices.
If you're interested in exploring the 639 Hz frequency, you can find audio recordings and music tracks featuring this frequency online. Keep in mind that while some people find value in using these frequencies for their spiritual and healing effects, there is limited scientific evidence to support such claims, so approach them with an open but critical mindset.