Fig.27 Jitter Spectrum, Bitwise System Zero processing 1kHz sinewave at 0dBFS (linear frequency scale, 0dB = 226.8ns).…
search
The last processor measured was the Bitwise Musik System Zero (reviewed in September 1992). At full scale the Zero had a smooth spectrum, with very few spikes and an overall jitter level of between 2.0 and 2.8ns. It maintained this performance until -50dBFS (worst case), where the number and amplitude of the periodic jitter components increased dramatically. The Zero's jitter spectrum is shown when driven by a full-scale signal (fig.27) and at -50dB (fig.28).
Sidebar 1: The Timing Problem
For the mathematically inclined, the signal/noise ratio (SNR) in a digital system is affected by time-base jitter in the following manner:
SNR = 20 log10(2 T PI F Square Root(2 F0/FS))
where: T = RMS jitter PI = 3.1416 F = signal frequency F0 = bandwidth of noise measurement (20kHz) FS = sampling frequency (352,800Hz for 8x oversampling)—Robert Harley
Sidebar 2: Politics
When John Atkinson and I first learned that the Meitner/Museatex LIM Detector was available for purchase, we were tremendously excited by the possibility of using it to measure jitter in digital audio processors and report the results in Stereophile. We were, however, aware of the political implications of buying a test-measurement system from a manufacturer who makes digital processors and competes with other manufacturers of digital processors. It is possible for a manufacturer to devise a test of questionable worth on which his product performs well but makes other…
The Jitter Game Revisited, April 1993 (Vol.16 No.4):
This "Follow-Up" also provides an opportunity to clarify a perplexing issue raised in the January jitter article. From those measurements, it would appear that processors with single-bit converters have much lower jitter than the more common 8x-oversampling units that use multi-bit DACs. Indeed, 1-bit converters typically have only a few picoseconds of jitter, rather than several hundreds of picoseconds or even several nanoseconds for multi-bit converters. Is the jitter performance of 1-bit machines intrinsically lower, thus "better…
The Jitter Game: an Update, October 1993 (Vol.16 No.10):
Since last January's "The Jitter Game," Stereophile has been able to measure and report on clock jitter in digital processors and CD players under review. In the intervening nine months, the technique has been improved with a second-generation Meitner LIM Detector (the jitter-measurement instrument), more sensitive measurement methods, and improved interpretation of the results.
First, Ed Meitner redesigned the LIM Detector. He added a "phase-detected" output that integrates the jitter, producing a flatter output with…
It was John Atkinson, that legendary ornithologist, who first pointed it out: "Have you noticed how frequently you see women using the iPod?"
I hadn't. I'd been so darn happy striding about the streets of New York listening to Tom Russell and Carla Bley that I hadn't been paying attention. Gimlet-eyed, I now began examining my fellow pedestrians for the telltale flash of the distinctive white-and-chrome player and the giveaway white headphone cable that announced the iPod's earbuds.
What an astoundingly acute observer of the human condition Stereophile's editor proved to be! Of…
One item that's invisible but indispensable is the iPod's operating system, which, I've been informed, is not of Apple design. PortalPlayer, a company that specializes in developing OSes for cellular phones, PDAs, and other streaming and wireless applications, designed the iPod's human interface. The iPod is so easy to use that it's obvious Apple chose the right company for the job.
Parts choices are said to have been made with an emphasis on sound quality, availability, and "time to market" considerations. Parts vetted include PortalPlayer's own MP3 decoder and controller chip, a…
What a thing to do!
The iPod is different from CD players, SACD players, DVD-Audio players, and pretty much any other consumer audio player in that it is a data-storage device. At the moment, it offers a variety of data-storage formats; but while I'm aware of no plans to do so, in the future it could accommodate others—even higher-rez options.
The iPod is different from CD players, SACD players, DVD-Audio players, and pretty much any other consumer audio player in that it is a data-storage device. At the moment, it offers a variety of data-storage formats; but while I'm aware of no plans to do so, in the future it could accommodate others—even higher-rez options.
The formats the iPod accommodates at the moment offer a wide range of options that balance disc storage space against sound quality. And this, not the iPod's size, is the revolutionary part: the consumer gets to choose which set of tradeoffs…
Sidebar 1: Specifications
Description: Portable data-storage device capable of playing compressed (MP3, AAC) and uncompressed (AIFF, WAV) digital audio files. Internal hard drive size: 30GB as reviewed; 10GB, 15GB, and 40GB also available. Frequency response: 20Hz-20kHz. Maximum output power: 30mW/channel.
Dimensions: 4.1" H by 2.4" W by 0.73" D. Weight: 6.2oz (176gm).
Serial number of unit reviewed: U23220DNNLY (auditioning); O2326CEFLV (measuring).
Price: $499. Approximate number of dealers: not specified.
Manufacturer: Apple Computer, Inc., 1 Infinite Loop, Cupertino, CA…
Sidebar 2: Bottom Liners
Great lines of numbers
all bright and shiny
all through the ether
some huge some tiny
all through the ether...
—Brian Eno, "Bottom Liners"
One of the most ballyhooed bits of news buoying the music industry recently was Apple's launch of its iTunes Music Store website, which offers AAC downloads of songs for 99 cents each. Despite the fact that the service is available only to owners of Apple computers (indeed, is accessible only through the iTunes4 software), which means that the 90% of computer users tethered to PCs can't use it yet (PC…