Listening In With Better Audio

By Pallab Chatterjee

The high profile discussion on new consumer products has been high definition-video and high-definition TV broadcast. The other end of the experience is starting to catch up with improved audio.

Since the shift from LPs and CDs has taken place towards downloadable portable audio data, there have been complaints from the listeners about the quality of the sound. The first two generations of digital sound were characterized by short data length (10-14 bits) and low sampling rates (22K-44K). These data sets were then compressed in dynamic range to minimize the data size. The resulting playback was a flat sounding audio file with typically only 60db of dynamic range, a smaller response range of 500Hz-14KHz, and of that only about 40db has been in the center range of 1KHz-5KHz.

To address these issues, most of the firmware/software-based systems at the recent Consumer Electronics Show and the National Association of Music Merchants (NAMM) show featured both longer data length (16-bit consumer, and 20-24 bit industrial/professional) and higher sampling rates (48K-96K consumer, and 96K-192K industrial/professional). The standard for most of the playback systems displayed in the new TVs and higher-end computer (gaming) surround sound systems is now 16 bit/48K. This is limited by the accuracy of the source material that has been digitized for download or on the Web and optimized for size rather than quality. The current Q1 2010 hardware that is in place typically will support a codec that can handle up to the 20-bit/96K data, and these are typically implemented in HDMI 1.3 systems which spec’s out for “lossless audio.”

The trend for newer designs is 24bit/192K hardware and typical application of a 24bit/96K software configuration for high-end systems. These high-end systems include AV products supporting the HDMI 1.4 specification (Blu-Ray, set-top Box, TV, etc.) and high-end gaming/content capture and editing computer systems. On the content creation and editing system side, to be able to handle these large data sizes and streams for editing (usually 8-32 simultaneous streams for mixing and editing along with video) the operationally minimum configuration is a quad core SMP system.

This need for the larger data sets, especially for creation and playback in 5.1 and 7.1 surround sound environments, has forced an advance in the microphone and portable recorder marketplace. For general podcast and home video/studio recording, most of the companies are now making their “standard microphones” available both as an analog XLR interface product and as a standalone USB2 interface product. The USB interface microphones are very stable, and produce decent quality 16bit/48K single channel audio targeted toward the voice band and the consumer “live performance audience capture” applications. Examples in the USB area are the new expanded products from Shure and Samson, which are sub-$300 products.

For higher fidelity in more controlled environments traditional mics (XLR input with phantom power) are being sent to 24b/96K and 24b/192K digitizing units that can support 2-8 channels of audio over the USB2 or Firewire 800 interface. Cakewalk and Roland had a number of new USB interface units which also feature 1/4″ jack inputs and MIDI. These units start in the $250 range and go up quickly in price for the rack-mounted systems for the professional marketplace.

For the high performance “live performance audience capture” application that is quickly becoming the standard for stereo HD video on demand or on the Web, Sony, Samson, Roland and Yamaha all have handheld full stereo 24b/96K recorders that support USB out. These devices, including the new models from Sony, support SD card memory in addition to the USB out. The USB data is single-stream, two-channel data. These products feature anywhere from 4 to 32 hours of battery life at the highest capture accuracy and range from the low $200 to several thousand dollars. The price spread is due to the quality of the microphones, circuitry used in the audio path and the choice of data converters.

The Samson features its standard condenser microphone and a standard multilayer board and commercial-grade data converters. These produce a very respectable 16-bit noise floor with the increased sampling rate. Sony offers multiple models, include its high-end units with some of “re-form-factored” studio microphones, pre-amps for the microphones, and industry standard Burr-Brown 24-bit, dual-channel ADCs. These are the same microphones, pre-amps and converters used in the discrete rack systems. (This solution is priced accordingly with the performance, and is on the lower end of battery life, but it can make it through a “studio day”).

The goal of the new systems is to bring portable and home audio to an equal user experience with portable and home video. At least you can hear the message more clearly.