No difference.
According to the query on Aiwen Education Network, "窪" is a variant of "窪", with the same meaning and pronunciation, and there is no difference. Chi is a horizontally blown bamboo wind instrument and a bass wind instrument. According to "Zhou Li·Zheng Xuan's Notes": "Chi, like a tube, has six holes." Guo Pu of the Eastern Jin Dynasty annotated "Erya": "The Chi is made of bamboo, with a length of four inches and a circumference of three inches. One hole comes out, and the inch is three points. It is called Qiao. It is blown horizontally. The smaller one is two inches in length." It is a horizontally blown bamboo wind instrument with 6 holes (including the upper outlet hole) and a closed bottom. Judging from the two large and small horizontally blown bamboo wind instruments unearthed from the tomb of Zeng Hou Yi in the early Warring States Period, they are similar to the characteristics of the chi described in the literature, but are different from the flute. Chi, vigorous, elegant and solemn, is one of the main musical instruments of ancient Chinese elegant music.