It is the brave men and women fascinated by analog-to-digital (A/D) and digital-to- analog (D/A) conversion that make audio a reality today. Dan Lavry, founder of Seattle-based Lavry Engineering, put his music bug and his science bug together early on. Now he spends his days ensuring that sound will come in and out of digital devices as transparently as the latest components will allow.
When did you first become interested in conversion?
Until the mid-'80s I was designing converters for different applications that weren't audio-related: medical electronics (early MRI machines), instrumentation and weighing scales for letters. Converters are simply the bridge from a world that is analog — such as blood pressure, the weight of a letter or sounds — to a world of technology that is built around computing. The reason conversion becomes so important is because of the shortcomings of analog. Before we got so computerized we had very low quality memory, and even today we don't have very good analog memory. In the past, for example, we put information on tape, which gets demagnetized on a car dashboard during a hot day; or vinyl, which is great until you wear it out or it gets scratched. Analog memory is very fragile. A lot of the analog memory shortcoming issues are solved in the solid world of numbers, which is where computers operate.
When did you first become interested in audio conversion?
When it comes to audio conversion, I had a lot of freedom in a couple of areas. One is that the absolute maximum peak level is not that critical. Usually you have some type of volume control anyway! You let the user change it so absolute maximum is not that critical. Also, the DC offset is not all that critical either (relative to many other applications). But audio conversion tends to be extremely demanding because of the dynamic range. The ear hears a very huge dynamic range. If you agree that a person can hear a 120 dB range — 1,000,000:1 range when you use common numbers instead of dB — then you can understand that the ear is extremely demanding. It was a big fight to get more and more dynamic range because the early converters were weak in that department — it was a struggle to get 16 bits. The other challenge is to achieve ultra low distortions. So I got interested in audio conversion because it was about music. I'm a musician and I play music every day. So here it was: an opportunity to combine what I like doing a lot, which is design, with another thing I like a lot, which is music.
Without getting too scientific about it, explain briefly what A/D and D/A converters are actually doing in the signal path.
