Lacquer cutting queries

[sifis1983]

Hi there!

While I'm searching information about my last research in my college I'm reading an article about lacquer cutting...

Well, I have some queries because, English is not my first language and I'm confused with a couple of terms...

So, I read this one:
Peak recorded velocities can reach as much as 50-60cm/s at high frequencies. The largest amplitude are at low frequencies and are of the order of 0.005cm.

The second sentence I can understand it.. It means the "space" that the bass take in a groove... But what about the first? I can't understand the term "velocity" here.. is it speed??? and what about the cm/s? is that "s" seconds?


Another issue I cannot understand is that..

The article refers the RIAA EQ and the amplitude compensation while recording.

It says : Below 1Khz the output to disc is attenuated and above is boosted.(ok! I can understand that..) The time constants are 75μs , 318 μs, 3180μs.

What are these numbers??? μs?? How this numbers connect with an EQ curve like RIAA...?


Please if anyone can explain these two problems, I would appreciate it....
Please try to explain in other words or in simple English.

Thank you!

[sifis1983]

Ok! I find another one !!

An article talking about recording stylus says:

"High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters."

Where the "centimeters" refers to ??

[markrob]

Hi,

Yes it is speed. s is seconds. So, velocity is expressed in cm/s. If you think about a stylus trying to trace out the shape of a sine wave (moving back and forth in a groove, the stylus is moving fastest as it crosses the zero amplitude portion of the cycle. It then slows from this peak to zero velocity as it reaches the top of the sine wave. Hope that makes sense.

Mark

[sifis1983]

thank you very much markrob for your reply!!

Yes! I can understand now... It's simply the speed of the recording stylus which is counted in cm/s...perfect!

So, in my third query
"High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters"

Does it means also the speed of the 1Khz signal in centimeters??

And what about these "time constants" on my second query?? do you have an explanation ?

[Woo40]

velocity = Denotes the speed or force with which a note has been struck

cm/s = speed measurement unit

i hope this helps.

[Serif]

thank you very much markrob for your reply!!

Yes! I can understand now... It's simply the speed of the recording stylus which is counted in cm/s...perfect!

Remember that the stylus might be said to have a speed of cutting even when it is cutting an unmodulated (silent) groove. The velocity of the stylus which is given in cm/sec, whether as a peak value or an RMS, is specifically talking about the speed of the stylus that is caused by the drive coils. There are only two directions for the mono head stylus - left or right (or up or down, in the case of a Hill and Dale recorder - aka "embosser" - actually doing impressing). Velocity means "speed in a given direction," since it is a vector quantity. However, we don't care that it is changing directions (accelerating). We are looking for the peak instantaneous velocity, or the average, RMS (root mean square) velocity (which happens at the furthest excursions, unlike the peak which, as Markrob explained, is at the origin)... You know how you can drive from Memphis, say, to Laredo, and average 50 MPH, but, when you were going through Amarillo at 4 am you know you were going at least 90. Your top speed might have been 101.6. Well, that's the peak velocity (since you had to be going in _some_ direction in order to be "going"). Speed and velocity are nearly identical. But Calculus will be found everywhere in disc recording - as will the irrational numbers. Specifically: Pi and root2. So, we might as well get ready for the three Calculean concepts of motion that are germane to cutting audio frequency signals at conventional disc revolution rates:

Displacement - concerns itself with the fact that cutter head low frequency response translates to wider excursions than does high frequency response - when the voltage of the signals is identical. By how much the stylus is "displaced" is of more of a concern than how quickly it is displaced, at low frequencies, for this reason. The cutter head is a velocity transducer, meaning, it converts electrical input of alternating current into motion. The higher the frequency of the source signal, the greater the velocity _and_ the less the displacement (since time doesn't slow down for treble, there's no time to go all the way as far as the lower frequencies do - and less power, since the cutter head introduces a complex mechanical impedance which must be flattened with mechanical and/or electrical dampening - often in the form of some negative program feedback being summed with the positive).

Velocity - the speed in the direction orthogonal to either the drive coil or the blank disc (depending on head construction), whether positive or negative (speed).

Acceleration - the faster-than-midrange frequencies only usually last less than a second (cymbal crash, hi hat, clave, blip, etc...) but cause a lot of heat to be generated in the drive coils, since they require much more power to transduce. 5-7 Watts for Miami Bass. 150-600 Watts for stuff like the clap used by Zapp. or really clear high end on a loud cut. The acceleration must not be so great that it burns the drive coil - since this is possible, even when Helium is used to cool it, nor must it be great enough to create a radius of curvature which is smaller than the tip of the stylus which is likely to attempt to reproduce the pressing or "acetate." Even though coils sometimes get burned in pursuit of the loudest high fidelity response, it's easier for most lathes to cut a faster groove than a record player can trace.

So, in my third query
"High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters"

Does it means also the speed of the 1Khz signal in centimeters??

Should read 7 cm/sec peak velocity. The RMS of that monophonic standard is 5.0 cm/sec If the peak stereo cutting velocity is 5 cm/sec/channel, then its RMS would be 3.54 cm/sec/channel. Clear as mud.

And what about these "time constants" on my second query?? do you have an explanation ?

In this application, time constant refers to the corner frequency achieved with an RC network. The resistance R is measured in Ohms, and the capacitance, C, is measured in Farads. Interestingly (or not), the Farad can be measured in seconds-per-Ohm. Since we are dealing with microFarads, we end up with a value for the time constant that is measured in microSeconds. (The Ohms unit cancels itself out).

When you look at the RIAA pre-emphasis and de-emphasis curves, you will note that the corner frequencies are routinely given in microSeconds. The number of this unit will vary inversely with the number that is the measure of frequency. In this way, the lower the frequency, the higher the number of microSeconds. So, the three base bands, being 50 Hz, 500 Hz, and 2122 Hz, are 3180, 318, and 75 µs (http://en.wikipedia.org/wiki/RIAA_equalization).

Don't forget to include something on half-speed mastering and quadrophonic mono-groove recording. Those really illustrate the outer limits. Video, too, and the technology of which that contributed to the development of Direct Metal Mothering (I mean Mastering - hehe).


Servus,
Doug Intuit

[markrob]

So, in my third query
"High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters"

Does it means also the speed of the 1Khz signal in centimeters??

And what about these "time constants" on my second query?? do you have an explanation ?

Yes, you can use db to make speed comparisons. Tha this becuase most pickups respond to velocity. That is, the velocity of the stylus is converted to a voltage. So you can use the voltage formula for db = 20 X log (V/7cm/s).

The time constants refer to the frequenices in the RIAA curve where breakpoints in the response occur. 1/(2 x PI x TC) = Frequency. Where TC equals the time constant in seconds. For example, 75us equates to 2122 hz.

Hope that makes sense.

Mark

[markrob]

velocity = Denotes the speed or force with which a note has been struck

cm/s = speed measurement unit

i hope this helps.

That is incorrect. It really is speed. Speed is the scalar form of velocity which also takes into account direction. The velocity you are referring to is an electronic keyboard term. Because most electronic keyboards don't respond to actuall key pressure (polyphonic aftertouch aside), they typically measure the velocity of the keypress and use this as a rough measure of actual force (F=MA).

[Serif]

...

The time constants refer to the frequenices in the RIAA curve where breakpoints in the response occur. 1/(2 x PI x TC) = Frequency. Where TC equals the time constant in seconds. For example, 75us equates to 2122 hz.

Right, again, however, just to be clear, since I mentioned irrational numbers, above, this time, the presence of Pi is not due to the parts of the circle most often found in the study of disc cutting - the circular motion creating radians of rotation along the revolution of a round object. It is rather due to the quadrants of the imaginary numbers which appear as a consequence of resistance and capacitance, in this scenario (passive component eq network to achieve RIAA). This is why there is a letter, "j," in the expression of impedance. It is resistance, reactance, admittance, and susceptibility. Or some such assemblage of properties - more than R... Z, mon... Interesting how our perspectives are so similar but different. Complementary like doped semiconductors, mon...


Cheers,
- Chuck Spindle

[mossboss]

Great thread Brilliant input Keep it up Cheers

[sifis1983]

Many thanks to SERIF!!!

Your explanation is absolutely understandable and gives me a lot of information that I should use for my research...

But, as you explain things to me, more queries are borned into my mind..hehe

So, the same article that I'm reading says:
"Accelerations of many hundrends of "g" are possible at high frequencies, which highlights the requirement of low moving mass at the replay stylus."

What is this "g"? Is this something that counts the acceleration of the cutting stylus?

Thanks again ...
and sorry for the late reply...

[dubcutter89]

What is this "g"? Is this something that counts the acceleration of the cutting stylus?

"g" is the natural acceleration on earth (gravity) which is 9.81 m/s^2

physics tells us that force F = Mass m x Acceleration a

so if you have high accelerations and want to keep the force (record wear etc.) low you have to reduce moving mass...

Lukas

ps:

Should read 7 cm/sec peak velocity. The RMS of that monophonic standard is 5.0 cm/sec If the peak stereo cutting velocity is 5 cm/sec/channel, then its RMS would be 3.54 cm/sec/channel. Clear as mud.

should we make this the official lathetrolls reference level?

[sifis1983]

Ok! thank you for your reply... but I feel stupid now..

Of course! g=gravity!!

[Serif]

I might expound that, by "imaginary number," and the "j" factor with Pi, it is in the situation of filtering with electrical components that we have control over the lag and lead of phase of the waveform. The lag or lead-back, is created along the quadrant of the X axis, not unlike a piston in a cylinder which pushes back and forth causing circular motion, elsewhere - also, locomotive side rods move like this, as well. The rim of a turning wheel pulls up into the Y-axis direction, but in a negative path with respect to X, until it has to pull the X-bound object in its negative direction... Then it begins to undo the disposition in a rather circular way. (; But pistons and train coupling rods move the way they do because of real circles in their midst. Whereas, the phase of the electrical waveform, such as the analog of a pure sine wave, or the analog of the sound pressures of musical program, moves due to an imaginary circle, which is determined by the complex impedances (Z = R + jX; where R is resistance (to current) and X is reactance (the resistance to _change in_ current _or_ voltage)) of the interconnections. Disraeli Gears....


Normally, a number squared is positive, even if the number not squared was negative. -4 x -4 = (+)16. The imaginary number, on the other hand, is that number, i (to mathematicians), or j, to engineers (since I already stands for Current), which allows for the movement of an exponential factoring (x/2\) to equal a negative number. In the case of j/2\, it's -1. But this opens the dimensional door for movement backwards, as if caused by the turning of an imaginary, but controlling, wheel. Since all wheels are circles, Pi is helpful in solving the ways of dividing that motion.


So, disc cutting is using circles both literally, and metaphysically (almost). It is definitely using lines (spirals). As David Berlinski points out, in his, A Tour of the Calculus, lines are continuous - unlike the discretized measurements of numbers (e.g., digital audio). Lines touch with intimacy the points occupied by both the rational and the irrational number, without error (and, for that matter, without even trying). Numbers can only try, since there's just not enough space or time~! (...for writing down that many extra numbers to the right of the decimal) This is not unlike the difference between quantum and classical physic.




- Chuck Spindle