The Walkman is enjoying a 21st century update. But while Sony’s original cassette player, first introduced in 1979, began the age of portable music, the new $700 digital Walkman is aimed at buyers who desire quality over quantity. The new Walkman ZX1 quickly sold out after hitting Japanese stores in December. The product has since debuted in Europe and other parts of Asia, but a U.S. launch has not been announced.

While televisions and games remain Sony’s mainstay products in consumer electronics, the ZX1’s popularity does highlight a shift among some portable-audio buyers. The first digital-audio players managed to store tens of thousands of songs in slim devices by compressing the audio files, a process that sacrificed sound quality. While sales of premium headphones have doubled in the U.S. over the past three years, “An entire generation missed the visceral emotion of listening to uncompressed audio,” said Sony Chief Executive Kazuo Hirai, during an electronics show in January.

Despite the current popularity, the ZX1 remains a unique product, with a bulky aluminum body that houses 128 gigabytes of high-speed storage for ultra-high-quality music files. Sony claims the format provides better sound quality than CDs, from deep bass tones to high-pitched sounds. High-resolution audio files contain more than three times as much data than CDs. Longer battery life also allows the Walkman to play high-end audio files and last around 16 hours, although that is still about one-fifth of the hours possible for portable compressed file players. And just as with TVs and smartphones, Sony currently faces a growing challenge from rival audio device makers.

Tento Koyama, a 19-year-old university student, is one consumer who is willing to pay extra for sound quality. In mid-May, Mr. Koyama lined up for one hour to take part in a headphone festival event in Tokyo where Sony’s ZX1 Walkman was displayed. “I think this one is the best Walkman in its history,” Mr. Koyama said, after listening to the ZX1 at a crowded Sony booth. “I don’t mind the price.”