I adjust the playback speed

Because Katakana is meant to add emphasis on a word. For example: Apple in Japanese is りんご or リンゴ("ringo"), either way works. There are many examples of using Katakana. Katakana is used for words that aren't covered by Kanji. 1) Onomatopoeia: mostly onomatopoeia are written in Katakana, like ワンワン("wan wan", woof woof). 2) Japanese companies: Japanese companies such as Nintendo have their names in Katakana. Nintendo's name can be written in either Kanji(任天堂) and Katakana(ニンテンドー). 3) animals/plants/minerals: although most of them have their own Kanji, if you don't remember the Kanji very well, it's better to write in Katakana. Like ゴリラ(gorilla). And to explain more about it. Katakana was used by Japanese Buddhist monks to transliterate Chinese texts into sutras. Kanji is meant for words of Sino-Japanese origin. Hiragana of Japanese origin(particles are frequently made of Hiragana), and Katakana is used outside of these origins.