Low cost synchronization
Alberto di Bene wrote:
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.
Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5. The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz. I'm measuring ~24998.5Hz against the
nominal 25000Hz. The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable. I've attached a
screenshot of the Baudline display.
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
John
In message 20050821.193225.53123034.cfmd@bredband.net, Magnus Danielson writes:
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
Which is what I recalled that you where saying. This is again my point, that
just because it is in one place, that is not universally true for all places.
The reasoning why people don't care as much should be fairly evident from the
discussion so far.
Just got off the phone with a guy who writes for the same paper as me,
has been teaching this stuff for ages.
As a regulation domain gets larger, (and "larger" is measured in
[MW * km * s] in this context), the inherent regulation mechanisms
may develop instabilities for which the only currently known cure
is a external frequency reference.
The reason they don't do that in NordPool is because they don't
think they are big enough to need it and because they have a
couple of HVDC lines to other larger regulation domains where they
can dump surplus or pull deficit on very short notice.
However, external frequency references are not the perfect cure because
they tend to trip more generators on faults in the network than the
traditional mostly MVAR (reactive power allocation) based regulations.
He said that the places he knew off that used it, had a two state
mode, in one state, the frequency locked state, the delta-frequency
(not delta-phase!) is limited relative to the external reference, and
an effort to keep the delta-phase low was purely manual. The other state
gives up on all external references and just tries to avoid a collapse
of the grid.
As usual with big systems, the big problem is that they never get to test
and they're never ready when they get a chance to collect experience :-)
Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
been done?
Well, since they don't encode UTC in the first place, they can just encode
leapseconds just like any other second :-)
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
BTW, measuring the 53rd overtone frequency may not give a clear picture of the
frequency deviations at the base frequency.
Even worse, it may not be a "real" overtone in the first place, it could be
a PWM tone from some regulated async motor.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 4308B7FF.6050308@erols.com, Chuck Harris writes:
No doubt, but even the best most gifted world class musician with
perfect pitch cannot resolve pitch to better than 1 cent. More usual
is around 4 cents.
That's actually not always true. Some musicians develop or have a
tinitus tone which allows the to cold tune their instrument with
much better than 1% precision.
It is theorized that people with "absolute hearing" actually reference
the tone to one or more tinitus tones which may be at the edge of
their hearing threshold but the disonances might not.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
From: "Poul-Henning Kamp" phk@phk.freebsd.dk
Subject: Re: [time-nuts] Low cost synchronization
Date: Sun, 21 Aug 2005 20:24:47 +0200
Message-ID: 58785.1124648687@phk.freebsd.dk
In message 20050821.193225.53123034.cfmd@bredband.net, Magnus Danielson writes:
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
Which is what I recalled that you where saying. This is again my point, that
just because it is in one place, that is not universally true for all places.
The reasoning why people don't care as much should be fairly evident from the
discussion so far.
Just got off the phone with a guy who writes for the same paper as me,
has been teaching this stuff for ages.
As a regulation domain gets larger, (and "larger" is measured in
[MW * km * s] in this context), the inherent regulation mechanisms
may develop instabilities for which the only currently known cure
is a external frequency reference.
The reason they don't do that in NordPool is because they don't
think they are big enough to need it and because they have a
couple of HVDC lines to other larger regulation domains where they
can dump surplus or pull deficit on very short notice.
However, external frequency references are not the perfect cure because
they tend to trip more generators on faults in the network than the
traditional mostly MVAR (reactive power allocation) based regulations.
He said that the places he knew off that used it, had a two state
mode, in one state, the frequency locked state, the delta-frequency
(not delta-phase!) is limited relative to the external reference, and
an effort to keep the delta-phase low was purely manual. The other state
gives up on all external references and just tries to avoid a collapse
of the grid.
As usual with big systems, the big problem is that they never get to test
and they're never ready when they get a chance to collect experience :-)
Interesting. Thanks for the report!
Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
been done?
Well, since they don't encode UTC in the first place, they can just encode
leapseconds just like any other second :-)
There is a simple method, just run a thad below 50 Hz (or 60 Hz) so that you
have the same number of cycles on 86401 seconds as you normally would for
86400 seconds. That would turn out to be about 49,999421303 Hz on average.
Thats -578,697 mHz or -1,157394E-5 relative.
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
BTW, measuring the 53rd overtone frequency may not give a clear picture of the
frequency deviations at the base frequency.
Even worse, it may not be a "real" overtone in the first place, it could be
a PWM tone from some regulated async motor.
That will be part of the energy, but the PWM would create sidebands around
the overtone. Diode-bridges, triacs etc. etc. all help to create overtones.
The current reactive load on the line will also affect the fundamental, and the
insertion and removal of capacitance on the power-grid will shift the phase.
If you thought the MW balance a headache, the MVAR balance is a real long
hangover all the time.
Cheers,
Magnus
In message 20050821.204040.123709461.cfmd@bredband.net, Magnus Danielson writes:
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
In Denmark they charge you $1000 extra to get a three-tariff meter :-(
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
I run a LynxOne sound card. It has clock in and out (75 ohms- TTL).
The clock can be 25 Khz to 27 Mhz. In its control software, it can use
a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, a word clock or a
X256 word clock.
I had considered using a synthesizer to locked up the sound card to the
rubidium during the ARRL frequency test back a few years ago. I worked
out everything in advance. I had a heart attack about 2 hours before
the contest - so I never got to work the contest...
I did not buy the card for the clock capability. It was bought because
it could handle 24 bit resolution and had digital and analog ins/outs.
You can also use multiple cards and the way they slave them, is via the
clock.
Brian N4FMN
John Ackermann N8UR wrote:
Alberto di Bene wrote:
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.
Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5. The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz. I'm measuring ~24998.5Hz against the
nominal 25000Hz. The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable. I've attached a
screenshot of the Baudline display.
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
John
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
----- Original Message -----
From: "Magnus Danielson" cfmd@bredband.net
snip
BTW, measuring the 53rd overtone frequency may not give a clear
picture of the
frequency deviations at the base frequency. Overtone spectras
experience quite
a different phase shift from the way it is produced by a number of
devices
which vector-add to become the seen frequency and phase. Turn on or
off a
strong producer of that frequency may shift that phase quite a bit
while the
fundamental is barly shifted.
Quite true, the majority of loads that produce high order harmonics
back into the grid are almost always varying considerably in the short
term-thus they produce short term variations in the resultant harmonic
spectra that renders the lines somewhat broader than you might think.
Ski lift motor drives are a good example of this. Such loads, without
adequate filterimg at the point of supply for the load, produce high
harmonic levels in the associated supply network, to the detriment of
any telecom cable network that happens to run parallel for significant
distances-as they always do in rural areas!
The old manual method that used to be used for power grid frequency
checking involved a comparison of two clocks, one driven from a
reference and the other from the grid itself-more usually the output
of a local generator in the days prior to strong grid linkages. The
comparison was typically done once or twice a day and appropriate
adjustments to the generation plant made to correct the grid driven
clock and keep its reading 'syncronised' to the reference clock.
I have here the remains of an attempt in the early seventies to bring
this type of system up to date - it comprised an HP 105 series quartz
reference, a K20- HP 5280A up down counter and an HP 5321B clock.
The up down counter was driven from 100 Hz signals derived from both
the 105B and the power grid. An HP 6933A D/A converter on the BCD
output from the counter had its plus/minus 10 volt output interfaced
to the generation plant. The 5321B clock reading was initialised from
the local time service(radio time pips) and then used to fine tune the
control system (D/A conveter to generator coupling) so the up down
counter stayed at or near zero reading and grid time ran in sync with
national standard time.
I dont know how successful this system was but I think it was in
service for several years.
I have the up down counter and the D/A converter almost fully
operational again- but only have parts ratted circuit boards from the
5321B clock and I never got the 105B.
DaveB, NZ
--
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Poul-Henning Kamp wrote:
In message 20050821.204040.123709461.cfmd@bredband.net, Magnus Danielson writes:
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
In Denmark they charge you $1000 extra to get a three-tariff meter :-(
Here in the UK we have "Economy 7" (it should be renamed "Rip-off 7")
where electricity is sold cheaper overnight. As far as I know, there is
no installation fee for that, but if you have "Economy 7" you pay more
for electricity during the day. So unless you make heavy usage overnight
(as one does with electrical storage heaters), it is not a good idea.
My meter, uses a clock that used to keep accurate, but which is now
usually wrong.
Whether the meter uses the 50Hz for timing I do not know, but there is
battery in there too. It may be wrong since the battery has failed and
so the clock stops when there is a power failure, or it might be low in
voltage which means the clock runs slow.
But here at least, there is nothing very clever about how the time on
those clocks is kept. Which suits me, as sometimes I get electricity
cheap during the day now!
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
Hi Poul,
As a musician myself, with marginal perfect pitch, I can cold tune to
about 7 cents absolute pitch on a 440 A, and much closer with relative
5ths. So basically, just using my ear, I can tune a fiddle so I won't break
anything, but I wouldn't be any fun to play with ;-) Oddly enough, I played
guitar for years, and didn't know I could do this until I learned to play a
fiddle.
However, I have never, ever heard of anyone that could prove to
do better than 1 cent. Do you have any reference to your claim? Perfect
pitch has always been something that has fascinated me, if only because
of the total unlikeliness of the whole thing.
Also, a cent is not the same as a percent. A cent is 1/100th the distance
between two adjacent semitones (eg. C and C#). There are exactly
1200 cents in each octave. So, as you can see, the spacing between
cents is logarithmic.
I have tinitus, but for me it is a rushing noise with some tonal component.
It sounds sort of like gas running through iron pipe when the furnace kicks
in.... or perhaps a flute that is being blown into, but is just starting to show
hints of producing a pure tone.
Once I had a fever, that I was treating with aspirin, and I had an annoyingly
large tinitus tone, So I thought I would try and get a beat note with it,
purely in the interests of science, of course. On went the headphones,
and I adjusted a signal generator from well below to well above, and I could
never get a beat of any sort. And further, I could never even do a good
job of matching the frequency. I concluded that tinitus tones must be outside
of audio in some way.... but then, I was feverish at the time.
-Chuck
Poul-Henning Kamp wrote:
In message 4308B7FF.6050308@erols.com, Chuck Harris writes:
No doubt, but even the best most gifted world class musician with
perfect pitch cannot resolve pitch to better than 1 cent. More usual
is around 4 cents.
That's actually not always true. Some musicians develop or have a
tinitus tone which allows the to cold tune their instrument with
much better than 1% precision.
It is theorized that people with "absolute hearing" actually reference
the tone to one or more tinitus tones which may be at the edge of
their hearing threshold but the disonances might not.
In message 4308F567.3020205@erols.com, Chuck Harris writes:
However, I have never, ever heard of anyone that could prove to
do better than 1 cent. Do you have any reference to your claim? Perfect
pitch has always been something that has fascinated me, if only because
of the total unlikeliness of the whole thing.
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.