What is the difference between Air Core Coil and core inductor?

1. With the same number of turns and volume, Air Core Coil's "inductance" value is much lower than that of solid inductors; air core inductors are more suitable for high frequency applications, while solid inductance has a serious frequency tendency; It is said that the hollow inductive reactance allows most of the audio or audio to pass, and the solid inductive reactance is selective, allowing only a part to pass.
                                                           Air Core Coil
2. The reason why these two kinds of inductive reactance are used is because of the need of audio and/or audio; in the frequency divider, the hollow inductive reactance is generally used in the preamplifier, which theoretically allows audio to pass through 20~20KHz; After the frequency, only the audio signals after "divided" such as 20~1KHz, 1K~10KHz, 10~20Hz, etc. are allowed to pass, so as to achieve the purpose of frequency division output.