Posted: 11/3/2009 7:23:00 AM EDT
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This popped into my head the other day, and wondered where it would go on here. Obviously this is completely theoretical, but suppose you have a (for simplicity's sake) 33 RPM record. On a turntable it plays normally. Now suppose you were to "uncoil" the record (yes, I realize they are not coiled) so that the grooves were all in tact, but it became a single linear track. A needle runs along the linear track at a constant speed, starting from the same spot it would on the record (towards the outer edge) thus producing sound from the grooves. Will there be an audible time-stretch effect (continuous change of pitch and tempo)? If so, in which direction (will the tempo and pitch increase or decrease as time passes?) I am excluding my hypothesis in this post as an attempt to dissuade it from influencing others' opinions ETA: A drawing  |
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Yes, the tempo and pitch will increase incrementally as you move along the track. On a regular record, the outside edge of the disc has a greater velocity than the inside edge, causing it to be recorded at a higher rate of speed.
On the disc itself, the track was recorded in the same fashion it is played back (turning at a constant 33 rpm), which is why there is no distortion under normal circumstances. I don't fucking know, that's a stumper..... ETA: Yes, the outside edge has more distance to cover to make one complete revolution? Thus decreasing the tempo and pitch as the needle moves along the straightened track? Or is the surface of the record moving at the same velocity throughout its surface area? |
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If the needle runs at the same speed, it will only play "the same as on a regular record" at one point of the record... that is assuming it ever hits the proper speed (if you run it too fast or slow, it never will).
The outside part of the record has more information, but it still revolves around at the same speed as the middle part of the record. By applying a constant speed to the needle on your hypothetical situation, you're not accounting or the variations in speed on a "regular" record. Thus it is theoretically possible to have both faster speed, regular speed and slower speed (chipmunk sound, regular sound and "duh debbil" sound) all at varying points of this hypothetical record. Another way to look at it is how fast the NEEDLE would need to physically move if there was a magical record player that didn't spin the records, but instead moved the needle. On the outer edges, the needle would be covering a lot more ground than near the middle. |
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Quoted: The pitch and speed of playback would continuously rise as you approach the end of the track that used to be closest to the center of the disk. This is my hypothesis, too, as a point closer to the edge of the record will be traveling at a higher speed than a point closer to the center, and the initial carving from the recording is done on the aluminum disc is done at (usually) a constant tempo The recording process would "involuntarily" account for the change in speed, if that makes sense.. |
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Quoted:
The pitch and speed of playback would continuously rise as you approach the end of the track that used to be closest to the center of the disk. Ok I'll finally get this edited correctly... 
On a pressed record the linear speed changes depending on how far away from the center the track is. This is compensated for during the cutting process but if you stretch the track out and play it at a constant linear speed rather than a constant angular speed then the pitch will change during playback. As an aside, one side effect of this is that the earlier tracks on a record (toward the outside edge) have higher fidelity/audio quality than the inner tracks due to the greater linear speed in that part of the record. In the days of vinyl albums bands/producers/record companies often tried to arrange their albums so that more popular or expected hit songs would be in the first and second tracks on each side of the album. |
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The inside track is moving slower than the outermost track (the inner track is covering a shorter distance in the same amount of time). When they make records, this is taken into account as the rotational speed, as far as I am aware, doesn't vary and is independent of the needle's position.
If you could simply unwind a record's entire track without distorting it and run a needle at a constant speed over the entire length, the output would slow down rise because the inner tracks are made to include the increased decreased speed of the inner most track. If you sped up slowed the needle in proper relation as you approach the "inner track" in the straight line, you'd avoid the distortion. ETA: My brain switched as I was typing again for some reason 
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Quoted:
The inside track is moving slower than the outermost track. (It's covering a shorter distance in the same amount of time). When they make records, they take this into account as the rotational speed, as far as I am aware, doesn't vary and is independent of the needle's position. If you could simply unwind a record's entire track without distorting it and run a needle at a constant speed over the entire length, the output would slow down speed upbecause the inner tracks are made to include the increased reduced speed of the inner most track. If you sped up slowed the needle in proper relation as you approach the "inner track" in the straight line, you'd avoid the distortion. |
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Quoted:
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The pitch and speed of playback would continuously rise as you approach the end of the track that used to be closest to the center of the disk. This is my hypothesis, too, as a point closer to the edge of the record will be traveling at a higher speed than a point closer to the center, and the initial carving from the recording is done on the aluminum disc is done at (usually) a constant tempo The recording process would "involuntarily" account for the change in speed, if that makes sense.. Let's say the circumference of the outer edge is 20" (I'm making this up) and the circumference of the inner edge of the track is 5". A point on both of these edges would return to its origin just under every two seconds, meaning the outer edge is going 20" every ~2 seconds and the inner edge is going 5" every ~2 seconds. But your right, the tone/tempo should increase on the "straightened" track. Right? |
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Quoted:
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The inside track is moving slower than the outermost track. (It's covering a shorter distance in the same amount of time). When they make records, they take this into account as the rotational speed, as far as I am aware, doesn't vary and is independent of the needle's position. If you could simply unwind a record's entire track without distorting it and run a needle at a constant speed over the entire length, the output would slow down speed upbecause the inner tracks are made to include the increased reduced speed of the inner most track. If you sped up slowed the needle in proper relation as you approach the "inner track" in the straight line, you'd avoid the distortion. Yeah, I was editing at the same time, you just beat me to the submit
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Interesting question, simple answer. Let's say you have a record that is a 12" circumference, and that you recorded a track on this record so that at one revolution per second (RPS), it made one "beep" sound every second. The "beeps" would be found in a straight line along the radius of the circle (a straight line from the center to the edge) because regardless of where you are along that radius, one Rev Per Second (RPS) is one RPS. A given point on the outer edge of the record is moving faster to make the rev than a point at the inner edge. So imagine that this record has a white line drawn on it to represent the location of the beeps. When you "unwind" the coil, the beeps at the outer edge will be 12 inches apart, where one RPS = 12 inches per second. As you move toward what would be the center of the spiral, the beep points would get closer together because the needle isn't having to cover as much distance to make the 1 RPS trip. Your straight line would look like this:
o..........o.........o........o.......o......o.....o....o...o..o.o If you travelled that line at a constant speed, the beeps would get closer together, or you would experience the "chipmunk effect" on a music track. That is all. ETA: edited to make the explanation a little more coherent. |
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The outside of the record is moving faster (in linear in/s or cm/s) than the inside at a given RPM, and the impressions are spaced further apart to preserve the audio. Playing the disc at a constant linear rate will result in the audio slooooooowwwwwwwiiiiiiiinnnnnnnnggggggg dddddddooooooooooowwwwwwwwwnnnnnnnn as it gets closer to the 'edge'.
ETA: Misread the question, been so long since I have seen a record I thought 'normal' starting was in on the inside. Playing it at a constant speed starting from the outside in would result in an increase in speed and pitch. |
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The outer grooves have exactly the same amount of information on them that the inner grooves do. The outer groove's circumference is at least twice as long as the inner groove's. They therefore have about 1/2 of the information on them per unit of length than the inner grooves do. If made linear and kept at a constant speed......more information per unit of travel would be played as you get closer to the groove associated with the inner rings. Making the playback sound faster. |
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Quoted: pitch goes up CD's start at the inner track and adjust their rpm to keep the bit rate constant. CD's are different from records - you are correct on speed, but wrong on pitch - 1's and 0's are not analog you would be seeing the equivalent of an increased bit rate. The bit values would not change. On an analog recording the speed of the record matters because the rate of change matters. In the digital world, you'd get read errors as the spacing between the bits and words would be fubar.
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Assuming the needle starts at what was the center edge of the record, the pitch will decrease increase as the needle follows the groove. This is because the linear velocity of the needle is greater at the outside of the record under normal operation.
The required linear needle velocity to read the record properly would be the record's angular velocity, times the distance from the record's center that the track originally was, times 2*pi |
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The outside of the record does indeed spin faster but I have never known a record player spin faster or slower by arm with the needle's location. So I would say the change in speed of the record is accounted for when recording the record. Correct, but it's not specifically accounted for, it just is what it is. Refer back to my earlier example. If you have a 12" circumference record making one RPS, and you put down a track that has one beep per second (so one beep per second = one RPS) you will start putting down one beep every 12 inches and as you work to the center, you'll put them down closer together. It's not that you specifically accounted for the speed variance, it just occured while you were putting down the track. If you could mark the beeps, they'd be in a straight line. A similar example is for dyes. A red dye has to reflect only a certain wavelength of light to make the cloth (or whatever) appear red. When they make the dye, they don't think about the physics of light wave frequencies, they just make a dye that's red. The fact that it's only reflecting a certain wavelength of light is just a property of the dye. |
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In normal play, the linear velocity of the track is greater near the perimeter as this is a constant RPM, not constant linear velocity, system. Played as a linear track, at constant velocity, this would mean that as you got farther into the track, the pitches would increase relative to the earlier (outer) parts of the track. The recorded audio would slowly speed up and raise pitch. As a point of interest, LaserDisks came in two separate recording formats: CAV (Constant Angular Velocity), with the disk running at a constant RPM all the time, and CLV (Constant Linear Velocity) where the disk rotates slowest when reading the outer regions and fastest when reading the inner regions. CLV gave greater play time per side (1 hour vs. 1/2 hour) but CAV disks had the advantage of absolutely perfect freeze-frame and slow-motion capability. Incidentally, CDs, DVDs, and Blu-ray disks also use a CLV system. CJ |
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Rise in pitch. The record plays from outside in. As you get closer to the center, the circumference is smaller, so there's more information per revolution, IOW, there's more music in a shorter distance of needle groove. If you uncoil it and play in a straight line at a constant speed, pitch will rise. |
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Quoted:
Interesting question, simple answer. Let's say you have a record that is a 12" circumference, and that you recorded a track on this record so that at one revolution per second (RPS), it made one "beep" sound every second. The "beeps" would be found in a straight line along the radius of the circle (a straight line from the center to the edge) because regardless of where you are along that radius, one Rev Per Second (RPS) is one RPS. A given point on the outer edge of the record is moving faster to make the rev than a point at the inner edge. So imagine that this record has a white line drawn on it to represent the location of the beeps. When you "unwind" the coil, the beeps at the outer edge will be 12 inches apart, where one RPS = 12 inches per second. As you move toward what would be the center of the spiral, the beep points would get closer together because the needle isn't having to cover as much distance to make the 1 RPS trip. Your straight line would look like this: o..........o.........o........o.......o......o.....o....o...o..o.o If you travelled that line at a constant speed, the beeps would get closer together, or you would experience the "chipmunk effect" on a music track. That is all. ETA: edited to make the explanation a little more coherent. Yup. The man put this very well. |
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Since the record turns at a constant angular velocity, for a given tone the arc length of the wave form at the outer edge of the record is greater than at the inner edge.
If you straightened the groove out and ran in under a needle at a constant linear velocity the beginning of the track would contain the long period wave form and the end would contain the shorter period waveform. The pitch would sound low at the beginning and higher at the end. |
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Good question. I guess the pitch would be higher or lower depending upon what speed you used to play back the linear record.
If you used a linear speed that equaled 33.3 RPM for a record then the first half of the record would have a lower pitch that rose at a steady rate until the middle of the linear track where it would be the normal pitch and then it would continue to raise until it was really high at the end of the line. |