FIG. 1: National Semiconductor''s sound room is completely isolated and acoustically treated. The finest consumer speakers are used to evaluate the performance of devices built with the company''s audio chips.
Audio technology has come a long way since the days of vacuum tubes, though some still believe that tubes produce the best sound. In most applications, however, solid-state electronics have brought high-quality sound to consumers and audio professionals alike.
For the last 30 years, National Semiconductor (www.national.com) has been at the forefront of analog audio electronics, designing and building integrated circuits (ICs, or “chips”) that are used in everything from A/V receivers to mixers to cell phones. In the mid-1990s, the company created a division dedicated to producing audio chips of the highest possible quality, and the most recent fruits of this labor blow just about everything else away.
For example, National's new LME line of op-amps achieve a total harmonic distortion plus noise (THD + N) of 0.00003 percent, a record low for this particular spec. Most high-quality op-amps have a THD + N of around 0.002 percent, roughly two orders of magnitude higher than the LME line. A THD + N in this range is fine in and of itself, but after a signal passes through ten such op-amps in a mixer, the final level of distortion and noise is much higher. By contrast, the final THD + N after passing through ten LME op-amps is still in the so-called triple-zero range (0.000× percent), much lower than that of even one typical chip.
Specs such as these are important, but the National team believes that they are only part of the story. Equally important is how the components sound in actual audio equipment. As a result, the team routinely builds preamps, power amps, and other audio devices with the new chips to see just how good they sound.
To help in this effort, National constructed a dedicated sound room, which was originally based on a recording-studio environment with Tannoy close-field monitors mounted in the wall where a mixer would be placed. But the team ultimately decided that a mid- to far-field setup would be more useful, so the space was configured more like an audiophile listening room (see Fig. 1).
The room is fully isolated with a floating concrete floor, airtight door, and acoustic treatments all around. Nothing can be heard outside, even when the volume is cranked, and a special air-conditioning system keeps the ambient noise level within very low. The engineers, many of whom are gifted with golden ears, listen on pairs of Wilson Audio WATT/Puppy 7s and B&W 802s and 801 Matrix 3s, all exceptional consumer speakers that reveal every nuance of any audio device's performance.
National's high-performance chips are made possible by innovations in two areas: design and process. In the design phase, circuit elements are laid out to enhance linearity and reduce distortion.
“Process” refers to the way in which circuits are actually constructed on a wafer. The LME line uses a process called VIP3 (Vertically Integrated PNP), a type of bipolar process that uses both PNP and NPN transistors. (PNP and NPN refer to the subatomic structure of the transistors and how electrons flow through them.) Unlike a standard bipolar process, in which the NPN transistors have high speed and bandwidth while the PNP transistors do not, VIP3 brings the speed and bandwidth of the PNPs up to the same level as the NPNs, avoiding the compromises that must otherwise be made.
The LME series is just starting to become available to manufacturers of audio products, and the company expects to develop many more super-high-quality audio chips in the near future. Thanks to a combination of design, process, objective measurements, and subjective listening, we can expect wonderful sounds to migrate from National Semiconductor's sound room to our studios.