cnbs30@vaxa.strath.ac.uk (04/06/91)
I am currently collating information on the use (or abuse!) of DSP for the marketing of digital audio. One look in recent Audio and Hifi magazines will confirm that digital signal processing (DSP) jargon is used for technical marketing purposes. CDs and DATs are described as having D/A converters, digital filters, 8 x's oversampling, references to quantisation, sampling, frequency responses and so on. And the latest references to bitstream; presumably the average buyer does not understand bitstream, but is impressed by this latest description, which makes his system better? How much of this is just marketing gimmicks? 4 x's versus 8 x's oversampling, can we hear the difference? Oversampling is described in some Hifi magazines as simply inserting extra samples between adjacent samples in order to increase the resolution? I always thought that oversampling was to avoid having to use expensive analogue filters at the input (anti aliasing) and outputs?? Is DSP terminology being used to hype up How can companies realise 20 bit outputs from D/As, when the data on a CD is only 16 bits? Just where is this extra information supposed to be materialising from? I recently saw a Sony advert in a tabloid newspaper, describing their latest CD as a state of the art DSP system. Does anyone have other examples of this techno-marketing strategy of companies. I am interested also in any information you may have received from suppliers or hifi stores, which can be best described as technical jargon marketing...... as in "Yes, this CD contains both a D/A converter and optical laser bit reader, and it uses 16 bit data". Dont all CDs? Once I have compiled some interesting information, I will make a posting to the news net. Thanks in advance for any contributions. -- ================================================================================ Bob Stewart |JANET: cnbs30@uk.ac.strath.vaxa EEE Dept. |E-MAIL: cnbs30%vaxa.strath.ac.uk@nsfnet-relay.ac.uk Strathclyde University|BITNET: cnbs30%vaxa.strath.ac.uk@UKACRL Glasgow G1 1XW |UUCP: cnbs30%vaxa.strath.ac.uk@ukc.uucp Scotland. | ================================================================================
mpurtell@IASTATE.EDU (Purtell Michael J) (04/08/91)
In article <1991Apr5.172259.11257@vaxa.strath.ac.uk>, cnbs30@vaxa.strath.ac.uk writes: > > I am currently collating information on the use (or abuse!) of DSP for the > marketing of digital audio. One look in recent Audio and Hifi > magazines will confirm that digital signal processing (DSP) jargon > is used for technical marketing purposes. CDs and DATs are > described as having D/A converters, digital filters, 8 x's > oversampling, references to quantisation, sampling, > frequency responses and so on. And the latest references to bitstream; > presumably the average buyer does not understand bitstream, but is > impressed by this latest description, which makes his system better? > > How much of this is just marketing gimmicks? 4 x's versus 8 x's > oversampling, can we hear the difference? Oversampling is described > in some Hifi magazines as simply inserting extra samples between > adjacent samples in order to increase the resolution? I always > thought that oversampling was to avoid having to use expensive > analogue filters at the input (anti aliasing) and outputs?? Inserting interpolated samples increases the sampling frequency which eases the constraints for the lowpass filter at the output. Sometimes the circuit that does the interpolation also increase the resolution (see below). > Is DSP terminology being used to hype up > > How can companies realise 20 bit outputs from D/As, when the data on a CD > is only 16 bits? Just where is this extra information supposed > to be materialising from? This is done by the interpolation circuit (usually a digital filter, ones I've read about are FIR filters). Imagine you have two samples with the values 1 and 2. Now you want to insert 7 values inbetween these for the 8 times oversampling. The values you'd probably use if you had unlimited resolution and were doing linear interpolation (for simplicity) would be: (real) (binary) 1.125 1.001 1.25 1.010 1.375 1.011 1.5 1.100 1.625 1.101 1.75 1.110 1.875 1.111 This is where the extra bits of resolution come from. Whether or not you can hear the difference is a debate I won't enter. :-) > -- > > ======================================================================== ========= > Bob Stewart |JANET: cnbs30@uk.ac.strath.vaxa > EEE Dept. |E-MAIL: cnbs30%vaxa.strath.ac.uk@nsfnet-relay.ac.uk > Strathclyde University|BITNET: cnbs30%vaxa.strath.ac.uk@UKACRL > Glasgow G1 1XW |UUCP: cnbs30%vaxa.strath.ac.uk@ukc.uucp > Scotland. | > ======================================================================== ========= -- -- Michael Purtell -- | "In a hundred years, | There's an Old Irish Recipe for mpurtell@iastate.edu | we'll all be dead." | Longevity: Leave the Table Iowa State University | -- The January Man | Hungry. Leave the Bed Sleepy. "slow is real" | Leave the Tavern Thirsty.