－What is the history of ATRAC development?

Suzuki : ATRAC made its debut in 1992 with the launch of the MiniDisc. In 1999, as a new feature of the MiniDisc called MDLP, we introduced ATRAC3, which delivered an improved compression ratio. And just as electronic music distribution started becoming popular, we introduced ATRAC3plus in 2002.

－Is the technology behind these codecs very different?

Suzuki : The basic technology is much the same. All codecs take as their input a PCM sound source. They perform signal processing on a fixed number of samples which are converted into frequency data and then compressed (encoded). At the other end, these steps are performed in reverse, so the data is decoded. After restoring the frequency data, signal processing reproduces the PCM sound source. With each codec, there's a difference in the number of samples used for frequency conversion: the higher the compression ratio, the larger the number of samples.

－In developing the codec, what was the most important thing for you?

Suzuki : The balance between audio quality and hardware resources.

Inoue : The ATRAC algorithm is implemented in hardware, an LSI, so the goal of our development is a tangible product. To achieve this, it's necessary for the LSI team and the algorithm team to coordinate their development work. That's one of the major differences between ATRAC and other codecs - not many other codecs have been developed in tandem with hardware.

Tsuji : It's a huge burden on the LSI if you try to make it process each and every single task that comes along. So it's important for the algorithm and LSI development teams to find the point at which there is a practical trade-off. For example, when developing ATRAC3plus, the algorithm that I was in charge of threatened to be a severe headache for the LSI team, but after several meetings we worked it out.

Inoue : Yes, our premise that hardware should efficiently process ATRAC encoding is especially important for us. In many cases, the encoding for other codecs is based only on software processing on a PC. But an essential feature of the MiniDisc, for example, is recording from the hardware unit. That's why, when we developed the specifications for ATRAC, we had to make sure the LSI could process the encoding at high speeds and with minimal power consumption.