How does a tape player know where the end of the song is and stops fastforward?
The heads are still lightly in contact with the tape, so it can pick up the music. Electronics in the tape deck look for periods of extended silence to stop the tape mechanism.
Some albums don’t have definitive silent breaks between songs, and the ‘search’ mechanisms won’t work on them. Other songs have silent passages in the middle which will confuse the search mechanism.
Okay, dhanson, here’s another for you. Since one revolution of a full tape passes a lot more tape through the tape heads than a revolution of a tape near the end (empty), how does the tape player know how fast to spin the tape hub? Seems like it would be easy if the tape had sprocket holes like a film and you regulated the speed at the head location with cogs, but it looks to me like the drive mechanism on a tape player is on the wheel itself. What’s up with that?
Only the “pulling” side is powered. the other is left free so the tape unwinds at whatever rate it needs to.
A normal cassette tape (as well as a video tape) does not go past the tape heads at a constant speed.
However, each section of tape goes through the play process at the same speed as it went through the record process, so even though the speed isn’t constant, it still sounds correct.
I don’t think that is correct. The cassette speed is 1 7/8 IPS and is dictated by the capstan/pressure roller. If it works anything like a reel-to-reel the feed and take-up reels pull the oposite directions via a slip clutch with the capstan pulling the tape through at a constant speed.
The speed of the tape (1 7/8 IPS) is controlled by pinching the tape between a rubber wheel and a thin steel roller. The steel roller is what goes through a little hole in the plastic case, right behind the tape. When you play, the rubber wheel presses against it and holds it tight, controlling the speed. The hub turns enough to keep some pressure to wind the tape, but not actually pull it through.
Don’t forget that three-head tape decks (one erase head, one record head, one playback head, in that order) usually have TWO capstans and pinch rollers, one on each end of the array of heads.
This is to ensure a superior sound by ensuring that the proxomity of the tape surface to each head is optomised at all times. Two capstans also help to optomise a constant tape speed past the heads.
Knock softly but firmly, 'cause I like soft, firm knockers…
Ain’t no such thing as consistant playback speeds when it comes to consumer audio tape machines. Unless it’s crystal controlled, time coded or timebase corrected, you’re dependant on the vagaries of the mechanical motor and your power source, both of which are notoriously inconsistant.
Television production gear, on the other hand, must be accurate to within 1/60 of a second or the entire system falls apart. Try playing side-by-side a video recording and an audio recording of the same live event. Over the course of several minutes, you will notice an obvious sync drift. After an hour, you’re two tapes could be seveal minutes out of whack. Most professional film and video audio recording decks are slaved to a to a common timecode generator for sync.
In those instances where you see amatuer filmmakers recording audio on low-end, non-synced audio tape recorders, they’re depending on the sync to hold for the short duration of each take.
dwtno, you better check this better.
audio and video tapes record and play at a constant tape linear speed (and therefore variable angular cassette spindle speed. You can check this easily.
old audio records turn at a constant speed and therefore the linear groove speed varies.
CD audio is recorded at a constant linear speed and therefore variable angular speed
Sailor, those are the textbook theories on how these systems are meant to work. What dwtno was referring to is that analoge media like audio tape (and phonographs, for that matter) don’t have PLL (phase locked loop) speed correction circuitry like digital (video tape, DAT, CD, etc.). PLLs work by keeping an eye on the data rate coming off the tape, checking it against an internal clock, and sending a correction to the capstan motor if a change in speed is necessary.
Why, you may ask, would a change be necessary? As motors & other electronic components age, their performance varies. Having a PLL circuit constantly making corrections is more efficient than carting your VCR into the shop every time your capstan motor speed drops by ½%.
In 9 years of consumer electronics service, I must have seen the complaint “tape plays too slow/too fast”. Check out the wow & flutter specs on an analog tape deck compared to a CD player and you’ll see how hard it is for manufacturers to keep analog tape speed constant.
Some cassette drives do actually have something called a hall sensor (more modern versions use an optical sensor) to sense the general speed of the reels. While this does not accurately reflect the linear velocity of the tape, it does let the mechanism know when to slow the tape down during fast ff & rev, as the tape nears the end of the reel.
Is how that third paragraph was supposed to look.
I stand corrected! Thanks for the info.
Opus, I meant to address it to Singledad rather than dwtno but pasted the wrong name. My posting was a reply to his about tape speed.