On Thu, 6 Jul 2017 11:42:09 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:
>Den torsdag den 6. juli 2017 kl. 19.54.10 UTC+2 skrev Joerg:
>> On 2017-07-02 18:46, bitrex wrote:
>> > On 07/02/2017 06:15 PM, pcdhobbs@gmail.com wrote:
>> >> The 200C isn't the original 1939 model. It was the last tube
>> >> instrument HP sold (CRTs and PMTs apart) and was in their 1985
>> >> catalogue. (Yes, I have one.) ;)
>> >>
>> >> Cheers
>> >>
>> >> Phil Hobbs
>> >>
>> >
>> > Wow, that late? I'm trying to think of other 1930s era industrial
>> > designs that had such a long life cycle. GG1 locomotives? Iowa class
>> > battleships? GM straight six?
>>
>>
>> Sure there were. Like this:
>>
>> http://www.4roues-sous-1parapluie.com/EN/p-the_story_of_the_2CV.html
>>
>> I had a 1969 model for many years.
>>
>
>codename the POS :)
>
>there's also this
>
>https://en.wikipedia.org/wiki/Volkswagen_Beetle
Reply by Lasse Langwadt Christensen●July 6, 20172017-07-06
Den torsdag den 6. juli 2017 kl. 19.54.10 UTC+2 skrev Joerg:
> On 2017-07-02 18:46, bitrex wrote:
> > On 07/02/2017 06:15 PM, pcdhobbs@gmail.com wrote:
> >> The 200C isn't the original 1939 model. It was the last tube
> >> instrument HP sold (CRTs and PMTs apart) and was in their 1985
> >> catalogue. (Yes, I have one.) ;)
> >>
> >> Cheers
> >>
> >> Phil Hobbs
> >>
> >
> > Wow, that late? I'm trying to think of other 1930s era industrial
> > designs that had such a long life cycle. GG1 locomotives? Iowa class
> > battleships? GM straight six?
>
>
> Sure there were. Like this:
>
> http://www.4roues-sous-1parapluie.com/EN/p-the_story_of_the_2CV.html
>
> I had a 1969 model for many years.
>
> On 07/02/2017 06:15 PM, pcdhobbs@gmail.com wrote:
>> The 200C isn't the original 1939 model. It was the last tube
>> instrument HP sold (CRTs and PMTs apart) and was in their 1985
>> catalogue. (Yes, I have one.) ;)
>>
>> Cheers
>>
>> Phil Hobbs
>>
>
> Wow, that late? I'm trying to think of other 1930s era industrial
> designs that had such a long life cycle. GG1 locomotives? Iowa class
> battleships? GM straight six?
>
> Tonewheel organs just generated top ocatave sine waves too,
>
** Hammond are the best known example of tone-wheel organs and had no frequency dividers - just an amplifier.
The teeth on the wheels were shaped to create different waveforms.
..... Phil
Reply by Clifford Heath●July 5, 20172017-07-05
On 06/07/17 03:32, bitrex wrote:
> On 07/05/2017 08:47 AM, Clifford Heath wrote:
>> On 05/07/17 21:32, bitrex wrote:
>>> On 07/04/2017 11:41 PM, Clifford Heath wrote:
>>>> On 05/07/17 05:57, pcdhobbs@gmail.com wrote:
>>>>>> Engineers probably worked for years to design clever "DCOs" which
>>>>>> frequency-locked analog oscillators to a temperature stable reference
>>>>>> clock, divided down under microprocessor control.
>>>>>
>>>>> Way before microprocessors, there were "top octave generators",
>>>>> strings of dividers running off a strategically-chosen crystal.
>>>>>
>>>>> They were too accurate, so they sounded thin.
>>>>
>>>> More precisely, they were accurate to a rational (fractional) scale,
>>>> not to a well-tempered scale. So you lost all the single-digit Hz
>>>> variations. Also, the lower octaves were again all divided exactly
>>>> by two, so there was no "stretch tuning" the pianos are tuned.
>>>
>>> The top octave was likely tuned to 12th-root-of-two equal temperament,
>>
>> No - they were integer approximations of the required dividers.
>> The most widely used chips audibly diverged from equal temperament.
>> You can do the sums yourself:
>> <http://synthdiy.com/files/2001/mk50240.pdf>
>> <http://www.armory.com/~rstevew/Public/SoundSynth/TopOctave/topdividers.html>
>
> Yeah, as the 12th root of 2 is irrational you would have to truncate the
> real number somewhere into a rational approximation, and apply something
> like a Stern-Brocot tree to find the best approximation with the
> granularity you have available.
> <https://en.wikipedia.org/wiki/Stern%E2%80%93Brocot_tree>
It's trivial to find rational approximations using continued fractions.
Here's the output of my program, given the twelfth root of 2:
$ ~/bin/continued_fraction 1.059463095
Usage: ratvalue [number [maxnumerator]]
number defaults to PI, maxnumerator to 500
Rational approximation to 1.059463095000000
1 / 1 = 1.000000000000000 with error 0.059463095000000
10 / 9 = 1.111111111111111 with error 0.051648016111111
11 / 10 = 1.100000000000000 with error 0.040536905000000
12 / 11 = 1.090909090909091 with error 0.031445995909091
13 / 12 = 1.083333333333333 with error 0.023870238333333
14 / 13 = 1.076923076923077 with error 0.017459981923077
15 / 14 = 1.071428571428571 with error 0.011965476428571
16 / 15 = 1.066666666666667 with error 0.007203571666667
17 / 16 = 1.062500000000000 with error 0.003036905000000
18 / 17 = 1.058823529411765 with error 0.000639565588235
53 / 50 = 1.060000000000000 with error 0.000536905000000
71 / 67 = 1.059701492537313 with error 0.000238397537313
89 / 84 = 1.059523809523810 with error 0.000060714523810
107 / 101 = 1.059405940594059 with error 0.000057154405940
196 / 185 = 1.059459459459460 with error 0.000003635540540
> I guess the top-octave chips of the time were using counters that didn't
> have many "bits", so it sounded off.
The dividers on the MK50240 produced a scale in which three of the notes
are more than one cents flat (compared to the mean line - compared to
the tonic it was even worse).
But though that's easily audible to folk with ear training, it's the
LF beats that are notably missing; hence the extensive use of tremolo
in a weak attempt to make up for it. You can clearly hear that in
"Light My Fire". It's a classic sound, so we like it; but doesn't
resemble the sound of physical resonators.
Clifford Heath.
Reply by bitrex●July 5, 20172017-07-05
On 07/05/2017 08:47 AM, Clifford Heath wrote:
> On 05/07/17 21:32, bitrex wrote:
>> On 07/04/2017 11:41 PM, Clifford Heath wrote:
>>> On 05/07/17 05:57, pcdhobbs@gmail.com wrote:
>>>>> Engineers probably worked for years to design clever "DCOs" which
>>>>> frequency-locked analog oscillators to a temperature stable reference
>>>>> clock, divided down under microprocessor control.
>>>>
>>>> Way before microprocessors, there were "top octave generators",
>>>> strings of dividers running off a strategically-chosen crystal.
>>>>
>>>> They were too accurate, so they sounded thin.
>>>
>>> More precisely, they were accurate to a rational (fractional) scale,
>>> not to a well-tempered scale. So you lost all the single-digit Hz
>>> variations. Also, the lower octaves were again all divided exactly
>>> by two, so there was no "stretch tuning" the pianos are tuned.
>>
>> The top octave was likely tuned to 12th-root-of-two equal temperament,
>
> No - they were integer approximations of the required dividers.
> The most widely used chips audibly diverged from equal temperament.
> You can do the sums yourself:
> <http://synthdiy.com/files/2001/mk50240.pdf>
> <http://www.armory.com/~rstevew/Public/SoundSynth/TopOctave/topdividers.html>
Yeah, as the 12th root of 2 is irrational you would have to truncate the
real number somewhere into a rational approximation, and apply something
like a Stern-Brocot tree to find the best approximation with the
granularity you have available.
<https://en.wikipedia.org/wiki/Stern%E2%80%93Brocot_tree>
I guess the top-octave chips of the time were using counters that didn't
have many "bits", so it sounded off.
"DCOs" in synthesizers from the 1980s had counters with more resolution;
my Roland Juno (circa 1986) uses Intel 8253 16 bit PITs under uP control
to divide an 8 MHz crystal clock and sync the analog sawtooth generators
to that.
>>> Needless to say, simplistic digital dividers like the top octave
>>> generators do not produce any of these effects!
>>
>> Yeah, but I don't think that's the reason they sounded "thin", it was
>> mainly because linearly mixing simple square waves of different
>> frequencies but the same phase relationships just sounds bad.
>
> It does. But all the ratios in stretch tuning and equal temperament that
> are not rational numbers generate a lot of low frequency beats
> that create a kind of vibrancy that you just don't get with simple
> fractions.
On Tuesday, July 4, 2017 at 1:03:10 PM UTC-4, bitrex wrote:
> On 07/03/2017 09:54 PM, Phil Allison wrote:
> > bitrex wrote:
> >
> > ------------------
> >
> >>
> >> Tangentially related - the audio sine wave oscillator I've been using
> >> for several years is a solid state box labeled "LofTech"; manufactured
> >> by "Phoenix Audio Labs, Manchester, CT".
> >>
> >> It's mostly full of LM13600s and TL074s with date codes from the middle
> >> of 1986. I don't have a THD analyzer so I can't say what its specs are
> >> now in that regard; visually at least the sines it puts out look math
> >> textbook perfect on a scope. The brochure claims a maximum THD of 0.5%
> >>
> >> Unfortunately frequency stability isn't good - it's very drifty with
> >> time and temperature; sometimes 3-5 Hz up and down over time just
> >> sitting in a shop at room temperature, which is annoying. The brochure
> >> scan online doesn't say anything about drift specs so I don't know if
> >> that's normal for the product's design or if it should be serviced.
> >>
> >
> > ** See link:
> >
> > http://www.barryrudolph.com/recall/manuals/loftts1.pdf
> >
> > The unit has a single pot that sweeps the audio band, assuming it is a carbon track type, frequency stability WILL be poor.
> >
> > Firstly, the track has a large tempco plus the wiper will have some drift after setting. So it is not faulty.
> >
> > My bench oscillator use a dual gang WW pot with hundreds of turns plus it only covers a decade range. A rotary switch choses which one of five starting at 2Hz. Drift is very small.
> >
> > The all valve one I mentioned also has low drift, once it fully warms up, as the frequency determining bits are an air capacitor and MF resistors.
> >
> >
> >
> > .... Phil
> >
>
> Got it, thanks. Probably time to invest in something a little better.
I love my rigol DG1022, ~1 milli-Hz to 20 MHz. (Sine).
It has two channels with synchronous phase control for each.
(Well there's an align phase button you have to press.)
George H.
Reply by Clifford Heath●July 5, 20172017-07-05
On 05/07/17 21:32, bitrex wrote:
> On 07/04/2017 11:41 PM, Clifford Heath wrote:
>> On 05/07/17 05:57, pcdhobbs@gmail.com wrote:
>>>> Engineers probably worked for years to design clever "DCOs" which
>>>> frequency-locked analog oscillators to a temperature stable reference
>>>> clock, divided down under microprocessor control.
>>>
>>> Way before microprocessors, there were "top octave generators",
>>> strings of dividers running off a strategically-chosen crystal.
>>>
>>> They were too accurate, so they sounded thin.
>>
>> More precisely, they were accurate to a rational (fractional) scale,
>> not to a well-tempered scale. So you lost all the single-digit Hz
>> variations. Also, the lower octaves were again all divided exactly
>> by two, so there was no "stretch tuning" the pianos are tuned.
>
> The top octave was likely tuned to 12th-root-of-two equal temperament,
>> Needless to say, simplistic digital dividers like the top octave
>> generators do not produce any of these effects!
>
> Yeah, but I don't think that's the reason they sounded "thin", it was
> mainly because linearly mixing simple square waves of different
> frequencies but the same phase relationships just sounds bad.
It does. But all the ratios in stretch tuning and equal temperament that
are not rational numbers generate a lot of low frequency beats
that create a kind of vibrancy that you just don't get with simple
fractions.
Reply by bitrex●July 5, 20172017-07-05
On 07/04/2017 03:57 PM, pcdhobbs@gmail.com wrote:
>> Engineers probably worked for years to design clever "DCOs" which
>> frequency-locked analog oscillators to a temperature stable reference
>> clock, divided down under microprocessor control.
>
> Way before microprocessors, there were "top octave generators", strings of dividers running off a strategically-chosen crystal.
>
> They were too accurate, so they sounded thin.
>
> Cheers
>
> Phil Hobbs
>
Tonewheel organs just generated top ocatave sine waves too, but sounded
great because you could mix in different harmonics from wheels of
various sizes to do basic additive synthesis.
Then push the result through an overdriven tube amplifier and a rotating
speaker.
Still popular in all styles of music:
<https://www.youtube.com/watch?v=cYC5cUQMU8I>
Yes. Yesss....
Reply by bitrex●July 5, 20172017-07-05
On 07/04/2017 11:41 PM, Clifford Heath wrote:
> On 05/07/17 05:57, pcdhobbs@gmail.com wrote:
>>> Engineers probably worked for years to design clever "DCOs" which
>>> frequency-locked analog oscillators to a temperature stable reference
>>> clock, divided down under microprocessor control.
>>
>> Way before microprocessors, there were "top octave generators",
>> strings of dividers running off a strategically-chosen crystal.
>>
>> They were too accurate, so they sounded thin.
>
> More precisely, they were accurate to a rational (fractional) scale,
> not to a well-tempered scale. So you lost all the single-digit Hz
> variations. Also, the lower octaves were again all divided exactly
> by two, so there was no "stretch tuning" the pianos are tuned.
The top octave was likely tuned to 12th-root-of-two equal temperament,
same as most modern non-piano polyphonic instruments (and synthesizers)
> Needless to say, simplistic digital dividers like the top octave
> generators do not produce any of these effects!
>
> Clifford Heath.
Yeah, but I don't think that's the reason they sounded "thin", it was
mainly because linearly mixing simple square waves of different
frequencies but the same phase relationships just sounds bad.