What is sound

1. sequence of vibrations in varying pressure strengths

What is Fourier Transform

What is spectrogram

1. visualizing sound

   1. waveplot

      

   2. fourier transform (frequency domain)

      fourier transform is a function that gets a signal in the time domain as input and outputs its decomposition into frequencies

      

      

   3. A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time.

   

What is mel scale

1. result of some non-linear transformation of the frequency scale. This Mel Scale is constructed such that sounds of equal distance from each other on the Mel Scale, also “sound” to humans as they are equal in distance from one another.

   It partitions the Hz scale into bins, and transforms each bin into a corresponding bin in the Mel Scale, using a overlapping triangular filters.

   

   Mel-scale은 이러한 pitch에서 발견한 사람의 음을 인지하는 기준(threshold)을 반영한 scale 변환 함수이다. 위에서처럼 [Hz -> 음계]의 관계가 exponential하기 때문에 주파수를 바로 linear하게 다루지 말고, log함수를 통과시켜 mel scale로 바꾼다음, linear하게 다루자는 것이다.