He joined Malay Film Productions in 1952 as an office assistant. He was fourteen years old.
Kassim bin Masdor, born in Singapore in January 1938, had perfect pitch and an instinctive grasp of chord structure, and he spent his free hours on the soundstages watching the studio orchestras work. The musical director Yusof B. noticed his piano playing; Ramlee noticed everything else, and drafted the teenager into the music department.
What he became was the person who wrote Ramlee's music down. Ramlee composed intuitively — humming, testing lines on violin or saxophone, hearing the whole arrangement in his head. Kassim sat beside him at the piano converting those raw motifs into written orchestral charts, string arrangements and five-part vocal scores. Without him a substantial portion of the catalogue would exist only as memory.
He gave Panca Sitara its signature sound — the tight chord voicings and Latin-jazz colour that make Bila Larut Malam and Kwek Mambo sound the way they do. He arranged and directed the backing scores for Seniman Bujang Lapok, Labu dan Labi, Ibu Mertua-ku, Madu Tiga and Tiga Abdul.
After Jalan Ampas declined he became chief record producer and A&R head at EMI, and effectively built the next generation: Sharifah Aini, Sanisah Huri, Ahmad Jais, Rafeah Buang, Sudirman Arshad. His own compositions include Selamat Hari Raya for Saloma. His 1987 oral history at the National Archives of Singapore is a primary source across this archive — including the record that Saloma adjusted Ramlee's vocal melodies herself.
Beliau menyertai Malay Film Productions pada 1952 sebagai pembantu pejabat. Usianya empat belas tahun.
Kassim bin Masdor, lahir di Singapura pada Januari 1938, memiliki pendengaran nada yang sempurna dan kefahaman naluri terhadap struktur kord, lalu menghabiskan waktu lapangnya di pentas rakaman memerhati orkestra studio bekerja. Pengarah muzik Yusof B. menyedari permainan pianonya; Ramlee menyedari segala yang lain, lalu menarik remaja itu masuk ke jabatan muzik.
Apa yang dijadinya ialah insan yang menulis muzik Ramlee ke atas kertas. Ramlee menggubah secara naluri — mendendang, menguji baris melodi pada biola atau saksofon, mendengar keseluruhan susunan di dalam kepalanya. Kassim duduk di sisinya di hadapan piano, menukarkan motif mentah itu menjadi partitur orkestra bertulis, susunan gesekan tali, dan skor vokal lima suara. Tanpanya, sebahagian besar khazanah ini hanya akan wujud sebagai ingatan.
Beliau memberikan Panca Sitara bunyi tersendirinya — susunan kord yang rapat dan warna jaz-Latin yang menjadikan Bila Larut Malam dan Kwek Mambo berbunyi seperti yang kita kenali. Beliau menyusun dan mengarahkan skor latar bagi Seniman Bujang Lapok, Labu dan Labi, Ibu Mertua-ku, Madu Tiga dan Tiga Abdul.
Selepas kemerosotan Jalan Ampas, beliau menjadi ketua penerbit rakaman dan ketua A&R di EMI, lalu secara berkesan membina generasi berikutnya: Sharifah Aini, Sanisah Huri, Ahmad Jais, Rafeah Buang, Sudirman Arshad. Gubahannya sendiri termasuk Selamat Hari Raya untuk Saloma. Rakaman sejarah lisannya pada 1987 di Arkib Negara Singapura menjadi sumber utama di seluruh pustaka ini — termasuk catatan bahawa Saloma membetulkan sendiri melodi vokal Ramlee.