Sony Corp. unveiled Thursday its plans to sell a 20GB Walkman digital music player in the United States by mid-August for under US$400 in an effort to cut into sales of Appleis popular iPod portable player.

The NW-HD1 (see photo below) will be the smallest 20GB player on the market, the company said. Storing some 13,000 songs, it is slightly larger than a credit card at less than a half inch thick. The device measures 3.5 inches by 2.44 inches by 0.54 inches thick and weighs 3.8 ounces. The device is more than two ounces lighter than the 40GB iPod.

Half the capacity of the 40GB iPod, Sony says it will store 13,000 song versus the Apple product at 10,000 tracks. Sonyis calculations are based on encoding using the Adaptive Transform Acoustic Coding for MiniDisc 3 (ATRAC3) compression system. The codec uses a data rate of 48Kbps versus Apple is Advance Audio Compression (AAC) compression rate of 128Kbps.

While a higher bit rate means better sound quality, a Sony spokesperson said ATRAC3 is more efficient at compression and is equal to that of the Apple iPod. The Walkman supports only Sonyis ATRAC3 and ATRAC3plus compression formats which is the standard format on Sonyis MiniDisc players and its Windows-only iConnecti online music store.

Song tracks compressed in ATRAC3 cannot be played on an iPod. Consequently, songs compressed in AAC using Appeis FairPlay DRM technology can also not be played on Sonyis NW-HD1 or any other device. The new Sony device also supports MP3, WAV and WMA files.

The NW-HD1 features a 1.5-inch backlit display and an on-screen display language which can be switched between Japanese, English, Spanish, French, German and Italian. The new hard-drive device connects to a compatible computer via a USB 2.0 digital interface for high-speed music transfers.

The player runs on a built-in rechargeable lithium-ion battery and will last for up to 30 hours when playing files encoded at the minimum supported bit rate of 48Kbps, according to the company. The battery life is three times longer than the iPodis, according to Sony. The battery life at 64Kbps or 128kbps encoding falls to 25 hours.

The hard drive for the NW-HD1 is made by Toshiba and also comes with 256MB of flash memory.

Sony plans to roll out the NW-HD1 in Japan on July 10 for US$490, in the middle of August in the US for less than US$400, and later this year in Europe.