What's the use of a 192 kHz sample rate?
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From: Robert Lacoste on 5 May 2008 07:18 "Green Xenon [Radium]" <glucegen1(a)excite.com> a �crit dans le message de news: 481becfe$0$5141$4c368faf(a)roadrunner.com... > Hi: > > Why does DVD-Audio use 192 kHz sample rate? What's the advantage over 44.1 > kHz? Humans can't hear the full range of a 192 kHz sample rate? I think that the answer is aliasing avoidance. Take it this way : - The audio band pass is limited to 16KHz, say 20KHz to get some extra marging for the most perfect ears on earth. - As far as I know ANY audio digitization circuit uses a low pass filter at around 20KHz, so even a 192Ksps ADC or DAC will be band pass limited to 20KHz signals, as there is absolutely no need to manage audio signals with a higher frequency. - If you use 44Ksps then you must insure that there is no power above 44/2=22KHz thanks to M. Nyquist, so your low pass filter must have a very sharp transition. As the filter will never be perfect you will get aliases. For example even if you use a 12th order filter (already difficult and expensive to build) then the attenuation will be "only" 72dB/octave, meaning that a 16KHz low pass filter will have an attenuation of only 50dB or so at 22KHz. And 50dB is not enough for good listeners as a -50dBc "noise" is clearly audible. - However if you use a 192Kbps sampling rate then the required performances on the low pass filter are drastically relaxed. This filter can keep a corner frequency at 16 or 20KHz, but even a 6th order filter will provide a at 86dB attenuation at 192/2=96KHz... And as a 192Ksps sampling rate is far cheaper to build than a very very good low pass filter... That's the beauty of oversampling... Does it make sense ? Cheers, Robert Lacoste www.alciom.com The mixed signal experts
From: Don Pearce on 5 May 2008 07:21 On Mon, 5 May 2008 04:15:59 -0700 (PDT), rajesh <getrajeshin(a)gmail.com> wrote: >On May 5, 3:46 pm, dpierce.cartchunk....(a)gmail.com wrote: >> On May 5, 4:05 am, rajesh <getrajes...(a)gmail.com> wrote: >> >> > Remember the shannon's theorem which places a >> > trade off between error correcting codes and bandwidth. >> >> Again, pure nonsense. Shannon's theorem >> never discusses error correcting codes AT ALL. > >hi pierce , > >BTW from which school did u learn DSP? Rajesh, please take some advice and don't do this. He is going to rip you to pieces and embarrass you badly. d -- Pearce Consulting http://www.pearce.uk.com
From: Don Pearce on 5 May 2008 07:27 On Mon, 5 May 2008 13:18:57 +0200, "Robert Lacoste" <use-contact-at-www-alciom-com-for-email> wrote: >"Green Xenon [Radium]" <glucegen1(a)excite.com> a �crit dans le message de >news: 481becfe$0$5141$4c368faf(a)roadrunner.com... >> Hi: >> >> Why does DVD-Audio use 192 kHz sample rate? What's the advantage over 44.1 >> kHz? Humans can't hear the full range of a 192 kHz sample rate? > >I think that the answer is aliasing avoidance. Take it this way : > >- The audio band pass is limited to 16KHz, say 20KHz to get some extra >marging for the most perfect ears on earth. > >- As far as I know ANY audio digitization circuit uses a low pass filter at >around 20KHz, so even a 192Ksps ADC or DAC will be band pass limited to >20KHz signals, as there is absolutely no need to manage audio signals with a >higher frequency. > >- If you use 44Ksps then you must insure that there is no power above >44/2=22KHz thanks to M. Nyquist, so your low pass filter must have a very >sharp transition. As the filter will never be perfect you will get aliases. >For example even if you use a 12th order filter (already difficult and >expensive to build) then the attenuation will be "only" 72dB/octave, meaning >that a 16KHz low pass filter will have an attenuation of only 50dB or so at >22KHz. And 50dB is not enough for good listeners as a -50dBc "noise" is >clearly audible. > >- However if you use a 192Kbps sampling rate then the required performances >on the low pass filter are drastically relaxed. This filter can keep a >corner frequency at 16 or 20KHz, but even a 6th order filter will provide a >at 86dB attenuation at 192/2=96KHz... > >And as a 192Ksps sampling rate is far cheaper to build than a very very good >low pass filter... That's the beauty of oversampling... > >Does it make sense ? > >Cheers, >Robert Lacoste >www.alciom.com >The mixed signal experts > Not a lot. As far as I'm aware there are NO ADCs that sample at the data rate of the output signal. For example the 44.1ksps ADC in my PC samples at 2.8224MHz. When you sample at that rate it is trivially easy to make a gently sloping analogue lowpass filter that guarantees a lack of alias products. All further filtering and decimation is done digitally, where it is easy. THAT is what oversampling is all about, not using a 192ksps sampling rate. d -- Pearce Consulting http://www.pearce.uk.com
From: rajesh on 5 May 2008 07:36 On May 5, 4:21 pm, nospam(a)nospam.com (Don Pearce) wrote: > On Mon, 5 May 2008 04:15:59 -0700 (PDT), rajesh > > <getrajeshin(a)gmail.com> wrote: > >On May 5, 3:46 pm, dpierce.cartchunk....(a)gmail.com wrote: > >> On May 5, 4:05 am, rajesh <getrajes...(a)gmail.com> wrote: > > >> > Remember the shannon's theorem which places a > >> > trade off between error correcting codes and bandwidth. > > >> Again, pure nonsense. Shannon's theorem > >> never discusses error correcting codes AT ALL. > > >hi pierce , > > >BTW from which school did u learn DSP? > > Rajesh, please take some advice and don't do this. He is going to rip > you to pieces and embarrass you badly. > > d > > -- > Pearce Consultinghttp://www.pearce.uk.com Here is the coz for mis interpretation of my opinions. I am not comparing two different discs of two different capacities at all. I am comparing, given the same high capacity disc, which sampling rate can cope better with errors. And the answer is the one with which is oversampled. say if u are comparing 44.1 kHz CD and a 196kHz DVD then they both cope with errors equally.there is no doubt about this. But then in the later case you are not comparing apples to apples.
From: Oli Charlesworth on 5 May 2008 07:36
On May 5, 12:18 pm, "Robert Lacoste" <use-contact-at-www-alciom-com- for-email> wrote: > "Green Xenon [Radium]" <gluceg...(a)excite.com> a écrit dans le message denews: 481becfe$0$5141$4c368__BEGIN_MASK_n#9g02mG7!__...__END_MASK_i?a63jfAD$z__(a)roadrunner.com... > - However if you use a 192Kbps sampling rate then the required performances > on the low pass filter are drastically relaxed. This filter can keep a > corner frequency at 16 or 20KHz, but even a 6th order filter will provide a > at 86dB attenuation at 192/2=96KHz... > > And as a 192Ksps sampling rate is far cheaper to build than a very very good > low pass filter... That's the beauty of oversampling... Oversampled conversion does not require one to *store* information at the oversampled rate. -- Oli |