Direct Cut Discs in the USA ??

[JayDC]

It seems you haven't understood the reasons why "high speed cutting", as described by you, makes no sense.

Excuse me sir, didn't know you are an expert on my experiences.

Lets review some basic facts:

1. The wavelength of a sine wave cut to disk is proportional to the speed of the turntable - the faster the turntable revolves, the longer the inscribed waveform on the record.

2. A different playback speed for the aforementioned sine wave will yield a different frequency - a slower speed will decrease the frequency, a higher speed will increase frequency

3. Cutting speed and lpi setting determine the maximum recording time for the disk

4. The physical size of cutting and reproducing stylii dictates the upper frequency limit - if you want to cut and reproduce higher frequencies, you can cut the original signal at higher speeds (= longer wavelenghts on the record), and then also play back the recording at a higher speed. But you will have less recording time.

1 and 3 are not a major concern... The physical size of cutting and reproducing stylii dictates the upper frequency limit is not even true, ask stan ricker..


You must have mis-understood.. I am talking about High Speed Dubbing, like on a dual tape recorder. Speed up the Source Material, and the Lathe Platter to cut a song in less time..

THe major problem I have notice, is the frequency shift, when you play something faster then the frequencies move up..

This means tha a 10Khz tone cut at 33rpm, and played back at 78rpm, could move up as much as 5Khz or more...

so if your cutting head cuts a good groove with a frequency range of 20hz to 12khz, you would lose the upper high end if you sped up the source and cut the record at a faster speed.

There for, The real limiting factor is the head.. Pitches, Lead Screws, LPI, etc can all be adjusted, some scullys can cut up to 600LPI.. If the head is 20hz -12khz, it will always be..

[subkontrabob]

sorry for going slightly off-topic....

Excuse me sir, didn't know you are an expert on my experiences.

dang, I make that mistake often..... for sure I'm no real expert.
I'll stay a novice of disk cutting for a long time.....

You must have mis-understood.. I am talking about High Speed Dubbing, like on a dual tape recorder. Speed up the Source Material, and the Lathe Platter to cut a song in less time..

Yep, that is indeed so, a misunderstanding, and what follows is that I usually make the impression of an ass....

Saving time makes perfect sense in the context of this thread.....

THe major problem I have notice, is the frequency shift, when you play something faster then the frequencies move up..

that's point number two in my list......

This means tha a 10Khz tone cut at 33rpm, and played back at 78rpm, could move up as much as 5Khz or more...

actually that's wrong, it's more than double the frequency. The ratio of the two speeds is 2,36, so 10 kHz cut @ 33 rpm would be 23,6 kHz @ 78rpm

so if your cutting head cuts a good groove with a frequency range of 20hz to 12khz, you would lose the upper high end if you sped up the source and cut the record at a faster speed.

not if you play it back at the same speed as it was cut. But if you slow down, it would happen for sure.

There for, The real limiting factor is the head..

that is my opinion too. It will probably be hard enough to design a head that can go up to 80 or even 150 kHz. Also, the stylus would have to endure much higher forces than usual.

The physical size of cutting and reproducing stylii dictates the upper frequency limit is not even true, ask stan ricker..

Are you sure? Many texts about cutting state this as a basic physical fact!


let's make a little calculation on this subject:
I found a formula for calculating wavelenghts in Dr Fritz Bergtold's book "Moderne Schallplattentechnik"

wavelenght (in micrometers) = RPM*groove diameter(cm)/1.9*Frequency (kHz)

if we assume that the resulting disc is to be played back at 33 rpm, and
want to cut four times faster than real time, we have to cut at 4*33 = 132RPM

If we want to reproduce frequencies up to 20 kHz, the head has to be able to cut 4*20 = 80 kHz. If we insert this into the equation, we get:

132*29/1.9*80 = 25.2 micrometers

that is one mil wavelenght. If we go further towards the center of the disc, at 15 cm:

132*15/1.9*80 = 13 micrometers = slightly more than half a mil

that's not very much...... please point out if I made errors!

.....and sorry if I came across arrogant

[JayDC]

.....and sorry if I came across arrogant

Quite alright, you can teach me math any time you like...