M
martin griffith
- Jan 1, 1970
- 0
I've been a long time meddler in (pro) audio, and over the last few
years I've been getting irritated by the stupid specmanship on audio
IC's.
My annoyance really started a year or so ago, when I was mucking
around with TI's PGA2310, a digitally controlled audio fader, with
the late Baz Porter, on a digitally controlled analogue parametric
equaliser. The PGA is a reasoable little IC for audio, but the stupid
way it was designed..... 0.5dB steps down to -95.5dB.
Who on earth would want to fade something that low. Most mixing
console faders tend to cut to infinity at -60dB... dumb, why not finer
steps, down to -60. It just seems so sensible. When I was a spotty
lad, -60dB was a tolerable level for distortion in a system!
On rec.audio.pro, ( a very busy NG,but very little wheat in the chaff
for me ) there was a thread about 384KHz PCM audio systems, and one
reply really hit the mark
I think it's this:
Message-ID: <[email protected]>
but I'm not too good on googling, so I post the whole message here,
Quote "
My name is Dan Lavry, and I hope you do not mind that I barge in. I do
want to say a few words on that 192Khz. As a designer, I have long
realized that faster sampling means less accuracy. You can get 1 bit
at a GHz, 8 bits at 100MHz, 12 bits at 30Mhz…. Nearly 24 bits at a few
Hz. Well, I am not suggesting to sample at 10Hz. We need to cover the
audio bandwidth. Going too slow is bad. Going too fast is also bad.
Let's face it, you want to say charge a cap, or settle an amp, and it
does dot happen at zero time. Nothing does. Weather you get there
exponentially or you have that step with some ringing… whatever it is,
if you wait till it settled you get it closer and more accurate. These
are practical limitations. The thing that gets me is that all the EE's
I talk to make jokes about 192Khz – a common one is "my dog can not
hear it". But many in the recording and mastering side are a part of a
different crowd. There seem to be a gap between the EE designer types
and the recording types. I am not suggesting that EE's are better or
worst. There have been times when the good ear is right, and the EE
learns new things. But there should be times such as right here and
now for the recording types to be open-minded. And folks, that 192KHz
is a crock.
I have wondered about how is it possible that a whole industry can go
in the wrong direction. After all, Few musical instruments will under
special cases yield a -50dB harmonic at 50Khz, and almost nothing at
100KHz. Experiments showing that special case required special mics
and gear. Most recording mics will not pick up a thing at 60khz… The
speakers will not play it, the ear will not hear it, no matter how big
the ego is!
So the sounds are negligible at those high frequencies, the mics will
not pick them, the speaker will not play it, and you can not hear it.
So how can such a crock take place? And let me assure you the folks
that made it happen at the semiconductor houses and workstation houses
did not include the EE department... I think it was and is about
making money. I talked to many engineers that stated privately that
they are not talking because they need their jobs! Other "did not want
to make waves", "stir the pot"…
So is everyone trying to cheat? Of course not. It started with 48Khz
better than 44.1, which is true. Also, while a bit excessive, 88.2 and
96KHz are in some cases a better compromise than 44.1. That is due to
the old FIR pre shooting (pre echo) that can happen under some cases
with a lot of processing. By the time you are at 60KHz it is so far
down you will not hear it, so 70Khz is a pretty reasonable place to
be. So after we have improved some as we went higher, the expectation
was than to continue upwards. Where does it stop? 384? Why not 1Ghz?
Oh well, the will be pretty bad, will it not?
But there is more to that than that "trendy upwards worked before so
lets continue". The common sense tells you that more is better. For
example, more pixels yield more detail. More bits gives better sample
accuracy. So if we take that analog wave, made out infinite points
connecting into a line, will we not benefit from a better "tracking"
of the wave? Well here is the news, and it is pretty old stuff, though
it may not be easy to grasp with simple common sense. More pixels for
better picture- yes! More bits for better accuracy (assuming
theoretical case - no noise) – yes! More sample density (higher sample
rate) for more accuracy –NO! This is the beauty of the sampling
theory. Nyquist did not say: We take more points and we will get
closer approximation. What he said – and it is a FUNDUMENTAL THEORY,
is that once we agree to deal with a limited bandwidth (called the
Nyquist bandwidth), all we need to do is sample at a tiny amount
greater than twice that bandwidth. This will yield 100% of the
waveform information in the data stream. We may need to filter a
signal (anti alaising) to make sure we do not have energy over
Nyquist, but than we are home free. Taking 4 times as many samples
does not yield 400% of the information. You can only have 100%! How do
you retrieve the information? You use a filter and it connects the
sample points in such a way that that you get the original wave shape.
A filter does not connect the dots (sample points) with straight
lines, or parabola… It recreates the original wave! You do not need to
help things with extra point in between. It buys you nothing!
I also see a lot of confusion regarding that Nyquist, upsampling,
oversampling, gradual filters… Some folks think that a 96KHz AD will
require a sharper anti aliasing filter than say 192KHz. This is
typically very wrong. The 96KHz or 192KHz AD refers to the OUTPUT RATE
of the converter. The antialias requirement is determined by the INPUT
SAMPLING RATE which is usually way beyond 192Khz. This days, most
modern AD's are running at input sampling rates of 3-12Mhz!!! DSD is
64fs and many mulibit IC's run even faster… So even with 50Khz audio,
Nyquist is so high the a gradual 3 pole will yield 120dB at the input
rate Nyquist. The outcome of the high rate modulator (input) is than
down-sampled to whatever – 44.1, 96, 192… Of course, when the sales
guys try to stick you with it they tell you need more bandwidth, but
they also ALL I saw regarding semiconductor and gear makers alike:
specs for 192KHz device are with A weighting – which states
(indirectly?) that you do not even need to measure flat to 20Khz. So
is it a crock? It is!
Theoretically, there is "no harm" in more points, and there is "no
added good". But as I pointed out, faster is less accurate! And yes,
you double the sample rate and the processing power requirement, and
so is the file size. These are serious draw backs! Don't you say you
do not care about file size: The DVD audio has 12 to 1 compression
(Dolby AC), We do not even get near a 1 to 1, and we want to push it
higher?
I realize that with all that reasoning and science and engineering,
someone is going to tell me that they hear it and like it. In fact,
someone told me that they still hear that high frequency in the
44.1KHz CD. I will not dignify that impossibility. If you hear some
distortion you like on the 44.1K CD, you did not need to go any faster
than 44.1KHz to generate it. I am not arguing against controlled
distortions (such as tube sound and what not). If you like it is fine.
It may be artistic decision. If you feel like you need to go to 1Mhz
than down to like it, fine. I think you are letting the gear control
you instead of the other way around, but fine! Just as long as I get
you to realize that you can get those distortions with a 44Khz… And we
do not all need to double the file size and processing power, and buy
new gear that is less accurate.
192 is a crock! 382 is a super crock! 88.2/96Khz is a bit excessive,
but not too far from a good rate. I too can glue a faster IC on the
board and make more money. My 192 DA prototype is not bad, but the
96KHz bits it by a lot.
Anyone telling you that more points will give better aproximation is
lacking lacking some know how.
Thanks for your patience.
Dan Lavry
Lavry Engineering
"
end quote
martin
"When all else fails, digitize everything, use fiber optic cable and enter a
whole new realm of problems."
<Found on the Rane tech page>
years I've been getting irritated by the stupid specmanship on audio
IC's.
My annoyance really started a year or so ago, when I was mucking
around with TI's PGA2310, a digitally controlled audio fader, with
the late Baz Porter, on a digitally controlled analogue parametric
equaliser. The PGA is a reasoable little IC for audio, but the stupid
way it was designed..... 0.5dB steps down to -95.5dB.
Who on earth would want to fade something that low. Most mixing
console faders tend to cut to infinity at -60dB... dumb, why not finer
steps, down to -60. It just seems so sensible. When I was a spotty
lad, -60dB was a tolerable level for distortion in a system!
On rec.audio.pro, ( a very busy NG,but very little wheat in the chaff
for me ) there was a thread about 384KHz PCM audio systems, and one
reply really hit the mark
I think it's this:
Message-ID: <[email protected]>
but I'm not too good on googling, so I post the whole message here,
Quote "
My name is Dan Lavry, and I hope you do not mind that I barge in. I do
want to say a few words on that 192Khz. As a designer, I have long
realized that faster sampling means less accuracy. You can get 1 bit
at a GHz, 8 bits at 100MHz, 12 bits at 30Mhz…. Nearly 24 bits at a few
Hz. Well, I am not suggesting to sample at 10Hz. We need to cover the
audio bandwidth. Going too slow is bad. Going too fast is also bad.
Let's face it, you want to say charge a cap, or settle an amp, and it
does dot happen at zero time. Nothing does. Weather you get there
exponentially or you have that step with some ringing… whatever it is,
if you wait till it settled you get it closer and more accurate. These
are practical limitations. The thing that gets me is that all the EE's
I talk to make jokes about 192Khz – a common one is "my dog can not
hear it". But many in the recording and mastering side are a part of a
different crowd. There seem to be a gap between the EE designer types
and the recording types. I am not suggesting that EE's are better or
worst. There have been times when the good ear is right, and the EE
learns new things. But there should be times such as right here and
now for the recording types to be open-minded. And folks, that 192KHz
is a crock.
I have wondered about how is it possible that a whole industry can go
in the wrong direction. After all, Few musical instruments will under
special cases yield a -50dB harmonic at 50Khz, and almost nothing at
100KHz. Experiments showing that special case required special mics
and gear. Most recording mics will not pick up a thing at 60khz… The
speakers will not play it, the ear will not hear it, no matter how big
the ego is!
So the sounds are negligible at those high frequencies, the mics will
not pick them, the speaker will not play it, and you can not hear it.
So how can such a crock take place? And let me assure you the folks
that made it happen at the semiconductor houses and workstation houses
did not include the EE department... I think it was and is about
making money. I talked to many engineers that stated privately that
they are not talking because they need their jobs! Other "did not want
to make waves", "stir the pot"…
So is everyone trying to cheat? Of course not. It started with 48Khz
better than 44.1, which is true. Also, while a bit excessive, 88.2 and
96KHz are in some cases a better compromise than 44.1. That is due to
the old FIR pre shooting (pre echo) that can happen under some cases
with a lot of processing. By the time you are at 60KHz it is so far
down you will not hear it, so 70Khz is a pretty reasonable place to
be. So after we have improved some as we went higher, the expectation
was than to continue upwards. Where does it stop? 384? Why not 1Ghz?
Oh well, the will be pretty bad, will it not?
But there is more to that than that "trendy upwards worked before so
lets continue". The common sense tells you that more is better. For
example, more pixels yield more detail. More bits gives better sample
accuracy. So if we take that analog wave, made out infinite points
connecting into a line, will we not benefit from a better "tracking"
of the wave? Well here is the news, and it is pretty old stuff, though
it may not be easy to grasp with simple common sense. More pixels for
better picture- yes! More bits for better accuracy (assuming
theoretical case - no noise) – yes! More sample density (higher sample
rate) for more accuracy –NO! This is the beauty of the sampling
theory. Nyquist did not say: We take more points and we will get
closer approximation. What he said – and it is a FUNDUMENTAL THEORY,
is that once we agree to deal with a limited bandwidth (called the
Nyquist bandwidth), all we need to do is sample at a tiny amount
greater than twice that bandwidth. This will yield 100% of the
waveform information in the data stream. We may need to filter a
signal (anti alaising) to make sure we do not have energy over
Nyquist, but than we are home free. Taking 4 times as many samples
does not yield 400% of the information. You can only have 100%! How do
you retrieve the information? You use a filter and it connects the
sample points in such a way that that you get the original wave shape.
A filter does not connect the dots (sample points) with straight
lines, or parabola… It recreates the original wave! You do not need to
help things with extra point in between. It buys you nothing!
I also see a lot of confusion regarding that Nyquist, upsampling,
oversampling, gradual filters… Some folks think that a 96KHz AD will
require a sharper anti aliasing filter than say 192KHz. This is
typically very wrong. The 96KHz or 192KHz AD refers to the OUTPUT RATE
of the converter. The antialias requirement is determined by the INPUT
SAMPLING RATE which is usually way beyond 192Khz. This days, most
modern AD's are running at input sampling rates of 3-12Mhz!!! DSD is
64fs and many mulibit IC's run even faster… So even with 50Khz audio,
Nyquist is so high the a gradual 3 pole will yield 120dB at the input
rate Nyquist. The outcome of the high rate modulator (input) is than
down-sampled to whatever – 44.1, 96, 192… Of course, when the sales
guys try to stick you with it they tell you need more bandwidth, but
they also ALL I saw regarding semiconductor and gear makers alike:
specs for 192KHz device are with A weighting – which states
(indirectly?) that you do not even need to measure flat to 20Khz. So
is it a crock? It is!
Theoretically, there is "no harm" in more points, and there is "no
added good". But as I pointed out, faster is less accurate! And yes,
you double the sample rate and the processing power requirement, and
so is the file size. These are serious draw backs! Don't you say you
do not care about file size: The DVD audio has 12 to 1 compression
(Dolby AC), We do not even get near a 1 to 1, and we want to push it
higher?
I realize that with all that reasoning and science and engineering,
someone is going to tell me that they hear it and like it. In fact,
someone told me that they still hear that high frequency in the
44.1KHz CD. I will not dignify that impossibility. If you hear some
distortion you like on the 44.1K CD, you did not need to go any faster
than 44.1KHz to generate it. I am not arguing against controlled
distortions (such as tube sound and what not). If you like it is fine.
It may be artistic decision. If you feel like you need to go to 1Mhz
than down to like it, fine. I think you are letting the gear control
you instead of the other way around, but fine! Just as long as I get
you to realize that you can get those distortions with a 44Khz… And we
do not all need to double the file size and processing power, and buy
new gear that is less accurate.
192 is a crock! 382 is a super crock! 88.2/96Khz is a bit excessive,
but not too far from a good rate. I too can glue a faster IC on the
board and make more money. My 192 DA prototype is not bad, but the
96KHz bits it by a lot.
Anyone telling you that more points will give better aproximation is
lacking lacking some know how.
Thanks for your patience.
Dan Lavry
Lavry Engineering
"
end quote
martin
"When all else fails, digitize everything, use fiber optic cable and enter a
whole new realm of problems."
<Found on the Rane tech page>
