間隔 and 頻度: the gap between events and frequency
Compare gaps between bus departures with visits per month, without converting a frequency into a fixed gap or visit duration.
Time between two events
間隔, read かんかく, refers here to the time between events. バスの発車間隔は十五分です。 says that bus departures are fifteen minutes apart.
前の音と次の音の間隔を測りました。 says that the gap between the preceding sound and the following sound was measured. The two events are explicitly identified.
How often within a period
頻度, read ひんど, identifies how often something happens. この店に行く頻度は月に二回です。 says that the person visits this shop twice a month.
練習の頻度を増やしました。 says that practice became more frequent. It does not say that each practice session was made longer.
A count and the actual gaps
月に二回行きます。 alone does not fix the dates of the two visits. They could be close together; check the dates separately to determine the gap.
発車間隔は長くなりましたが、乗車時間は変わりません。 says that gaps between departures became longer, but riding time remains unchanged. Departure spacing and time spent riding are distinct.
Does この店に行く頻度は月に二回です。 mean visits are always exactly fifteen days apart?
Show the answer and why
No. It supplies a count of two visits per month. Neither the visit dates nor the exact gap between them is stated.