maddog@athena.mit.edu (Matthew J Marjanovic) (06/03/90)
Is it possible?
Someone gave me a supposedly broken tape player to look
at, and while I was doing comparitive studies with CD recordings
I noticed that my CD player was running just a little bit slow:
everything was just a bit flat, and a good tape player would
perceptibly overtake the CD in about ten seconds.
I haven't opened up my player yet to snoop around, but what are the
chances of me being able to tweak it up to speed?
They player is a Garrard GCD-46 boombox deal, with the CD tray on top.
If there is a simple potentiometer in there labeled "Speed Adjust", what
can I use besides my ear to calibrate the machine? Are there any test
signals that a player produces (or is a calibration disc necessary?)?
I do have access to good quality oscilliscopes and the like, if I need them.
Thanks in advance for anything that will save me from
taking this in, and for getting this fixed before I
leave for home on Wednesday....
____________________________________________________________________
Matt Marjanovic | "He who has never envied the vegetable,
maddog@athena.mit.edu | has missed the human drama."
| -- E.M. Cioran
--------------------------------------------------------------------abl@dart.ece.cmu.edu (Antonio Leal) (06/03/90)
In article <1990Jun2.182334.21396@athena.mit.edu> maddog@athena.mit.edu (Matthew J Marjanovic) writes: > Is it possible? > Someone gave me a supposedly broken tape player to look > at, and while I was doing comparitive studies with CD recordings > I noticed that my CD player was running just a little bit slow: > everything was just a bit flat, and a good tape player would > perceptibly overtake the CD in about ten seconds. Have you considered the possibility that the tape player(s) may be running fast ? It's kind of hard to make quartz-oscillator digital circuits run slow (i.e. all the servo controls and digital-to-analog conversion in the CD), while it's very easy to have an analog controlled motor and belt system with all analog front end (i.e. the tape player) be a bit off. Then again, maybe the quartz oscillator _is_ out of whack, but I doubt it. Usually they are spec'd to a few p.p.m. (parts per million) precision, and if the capacitors in the circuit around the quartz go bad, it just does not run. Check it CD against CD, and tell us, huh ? Or just check the time elapsed count against a watch. -- Antonio B. Leal Dept. of Electrical and Computer Engineering Bell: [412] 268-2937 Carnegie Mellon University Net: abl@maxwell.ece.cmu.edu Pittsburgh, PA. 15213 U.S.A.
chuck@umiami.miami.edu (06/04/90)
In article <ABL.90Jun2233534@dart.ece.cmu.edu>, abl@dart.ece.cmu.edu (Antonio Leal) writes: > In article <1990Jun2.182334.21396@athena.mit.edu> maddog@athena.mit.edu (Matthew J Marjanovic) writes: >> Is it possible? >> Someone gave me a supposedly broken tape player to look at [...] > Have you considered the possibility that the tape player(s) may be > running fast ? > It's kind of hard to make quartz-oscillator digital circuits run slow[...] > -- > Antonio B. Leal Dept. of Electrical and Computer Engineering > Bell: [412] 268-2937 Carnegie Mellon University > Net: abl@maxwell.ece.cmu.edu Pittsburgh, PA. 15213 U.S.A. After all of this ... There is no way in the world that the CD player would play "slow" or "flat" because of the nature of the beast. If the disc spins at the wrong speed, you will get errors beyond belief (depending on how 'wrong' the speed is). If the data is clocking into the DAC at the wrong rate, you would get weird sounds or muting even. It is impossible for the pitch of the CD to be any different than when it was recorded to the disc, because the numbers cannot be pitch-shifted by a simple speed adjustment. Pitch-shifting in the digital domain is a fairly ugly computational process, usually handled by high-speed DSP chips. Anyway, the point is that the CD player in question here is not slow, the tape deck is fast, and you should look for the pot inside the tape deck to adjust this (if one even exists!). You should find that one CD is exactly in tune with another CD (as long as it's the same music... :-) ) because they all have the same digital master. Gosh, I really can ramble on... :-) -- =========================================================================== Chuck Urwiler University of Miami Music Engineering Voice & Keys chuck@umiami <<BITNET ADDRESS chuck@umiami.miami.edu <<INTERNET ADDRESS =========================================================================== Disclaimer: I only work and learn at this University. I don't speak for it!
rubin@polaris.cis.ohio-state.edu (daniel j rubin) (06/04/90)
>Is it possible? > >Someone gave me a supposedly broken tape player to look > at, and while I was doing comparitive studies with CD recordings > I noticed that my CD player was running just a little bit slow: > everything was just a bit flat, and a good tape player would > perceptibly overtake the CD in about ten seconds. > > >I haven't opened up my player yet to snoop around, but what are the > chances of me being able to tweak it up to speed? > >They player is a Garrard GCD-46 boombox deal, with the CD tray on top. > >If there is a simple potentiometer in there labeled "Speed Adjust", what > can I use besides my ear to calibrate the machine? Are there any test > signals that a player produces (or is a calibration disc necessary?)? >I do have access to good quality oscilliscopes and the like, if I need them. > I really do not think it is possible for a CD player to run slow and produce the lower and slower tones as does when a analog tape player runs slow. A CD contains digital data which has to be read in at the proper speed for the digital to analog converter to do its job properly. If you take a CD player and slow the disk down with your finger as it is playing it will produce gaps in the music which sounds like noise. My CD player was producing this noise so I opened it up to see if I could fix it and I just happened to rub my finger against the spinning CD and the noise got worse. I started playing around with the pots in the player and happened to find the one to fix the problem and now it works fine. I believe the problem with my CD player was that the disk was spinning just a tad bit too slow and it needed an adjustment and due to the fact it was playing too slow it produced what sounded like noise (missing data in the music, perhaps ?) not lower tones. Try adjusting the speed adjustment you found inside your box and see if it causes this in the CD output (I am assuming the speed adjustment you found inside your protable box is for the CD player and not the tape player). I do not know why your CD player is playing flat and I am just guessing what the exact problem with my player was based on what I found. I hope you can figure it out, it really sucks when you take something in to the repair shop and they charge you fifty bucks to make an adjustment somewhere. By the way if anyone out there has a Sony D-10 and there is something that sounds like excessive noise in the output (escecially with high notes and with songs at the end of the CD) the potentiometer I adjusted to fix the problem is the one located on the side of the actual moving mechanism containing the laser (if you take the back off the player you can't miss it, it is really easy to get to). Try adjusting it just a very slight bit either way and you may be able to fix the problem and save yourself a trip to the repair shop and some bucks. - Dan Rubin
dwn@swbatl.sbc.com (4007) (06/04/90)
In article <6378.26693284@umiami.miami.edu> chuck@umiami.miami.edu writes: >In article <ABL.90Jun2233534@dart.ece.cmu.edu>, abl@dart.ece.cmu.edu >(Antonio Leal) writes: >> In article <1990Jun2.182334.21396@athena.mit.edu> maddog@athena.mit.edu >(Matthew J Marjanovic) writes: >>> Is it possible? >> Have you considered the possibility that the tape player(s) may be >> running fast ? >> It's kind of hard to make quartz-oscillator digital circuits run slow[...] >> -- >> Antonio B. Leal Dept. of Electrical and Computer Engineering >> Bell: [412] 268-2937 Carnegie Mellon University >> Net: abl@maxwell.ece.cmu.edu Pittsburgh, PA. 15213 U.S.A. > >After all of this ... > >There is no way in the world that the CD player would play "slow" >or "flat" because of the nature of the beast. ... I agree the CD player cannot alter the pitch of the sound AS RECORDED, but it is possible that the recording process was defective when the CD was produced (especially if it's a digital re-master of an analog recording). This could result in a slightly flat recording. I've had a few record albums (vinyl, analog) that had just a single track that was "between" keys. -- name & address (this account) -> uunet!swbatl!dwn OR dwn@swbatl.swbt.com David Neill office -> 405-291-1990 -> uunet!swbatl!oktext!mktco Mgr - Mktg.(SWBTCo) home -> 405-749-1141 -> uunet!swbatl!oktext!frodo!david
mcmiller@uokmax.uucp (Michael C Miller) (06/04/90)
In article <6378.26693284@umiami.miami.edu> chuck@umiami.miami.edu writes: >question here is not slow, the tape deck is fast, and you should look for >the pot inside the tape deck to adjust this (if one even exists!). Well I don't think that there is a spped adjustment in the form of a pot on any deck. The motors I have seen in tape players have a small hole in the rear of the motor case. The adjustment is there. If you do try this DONT USE A METAL SCREW DRIVER TO ADJUST THE SPEED. You will have to use a recorded tone and a scope or by ear. If you use a metal tool, the speed will change everytime you remove the tool! I learned this the hard way. michael -- So , What was *REALLY* going on between Kukla, Fran and Ollie ??? < sans => mcmiller@uokmax.UUCP or mcmiller@uokmax.ecn.uoknor.edu > < '..this one goes up to eleven. Its ONE louder.' >
sorka@ucscb.UCSC.EDU (Alan Waterman) (06/04/90)
Sorry Chuck, but that is not quite right. The crystal occilator controls the speed of everything in the player, even the motor speed. If the crystal is slightly slow(I know it sounds impossible, but it DOES happen) then everything else will also be running slow.
gordonl@microsoft.UUCP (Gordon LETWIN) (06/04/90)
In article <6378.26693284@umiami.miami.edu>, chuck@umiami.miami.edu writes: > > There is no way in the world that the CD player would play "slow" or "flat" > because of the nature of the beast. ... > ...Pitch-shifting in the > digital domain is a fairly ugly computational process, usually handled by > high-speed DSP chips. This is wrong. Pitch shifting is easy. My first CD player was an inexpensive one and it had a pitch adjustment control on it. It's my guess that you can pitch shift just by changing the rate at which you feed samples to the DtoA convertor. CD players already have circuitry to adjust the rotation rate to keep the convertor FIFO happy, so I expect that if you just change your sample clocking rate the slight change of the disc rotation rate would occur automatically. Regardless of how it was done, my old unit, which I paid $400 for maybe 5 years ago did it, so it's not a big deal. Gordon Letwin
chuck@umiami.miami.edu (06/05/90)
In article <55024@microsoft.UUCP>, gordonl@microsoft.UUCP (Gordon LETWIN) writes: > In article <6378.26693284@umiami.miami.edu>, chuck@umiami.miami.edu writes: >> >> There is no way in the world that the CD player would play "slow" or "flat" >> because of the nature of the beast. ... >> ...Pitch-shifting in the >> digital domain is a fairly ugly computational process, usually handled by >> high-speed DSP chips. > > This is wrong. Pitch shifting is easy. My first CD player was an > inexpensive one and it had a pitch adjustment control on it. It's my > guess that you can pitch shift just by changing the rate at which you > feed samples to the DtoA convertor. CD players already have circuitry > to adjust the rotation rate to keep the convertor FIFO happy, so I expect > that if you just change your sample clocking rate the slight change of > the disc rotation rate would occur automatically. > > Regardless of how it was done, my old unit, which I paid $400 for maybe > 5 years ago did it, so it's not a big deal. > > Gordon Letwin As many of you have pointed out, I was wrong in my statements included within. Pitch shifting is *easy* when playing back CD's, cause all you do is change the sample rate. However, what I said was true for the disc speed, cause if you slow down just the disc speed, you end up with "noise" (which someone else has also realized in this discussion). As Gordon has pointed out in this article, you must change the actual sample rate of the entire system to make a pitch change. I have the feeling I was thinking of sample rate conversion, not pitch shifting. Anyway, I wasn't totally wrong... :-) The point is this - most CD players today (correct me if I am wrong, you guys are good at that... :-) ) use oscillators that are usually pretty damn exact anyway, so there's no reason to want to change it. I would rely on the pitch of a CD over the pitch of a tape deck any day, especially since the tape speed varies over the length of the tape, and the fact that the CD player is (supposed to be) accurate to 1/44100 of a second. I never thought this would be such a big thing... :-) -- =========================================================================== Chuck Urwiler University of Miami Music Engineering Voice & Keys chuck@umiami | This space for rent... e1mvqi9z@umiamivm | chuck@umiami.miami.edu | chuck@miavax.ir.miami.edu | =========================================================================== Disclaimer: I only work and learn at this University. I don't speak for it!
jj@alice.UUCP (jj, like it or not) (06/05/90)
In article <55024@microsoft.UUCP> gordonl@microsoft.UUCP (Gordon LETWIN) writes: >In article <6378.26693284@umiami.miami.edu>, chuck@umiami.miami.edu writes: >> >> There is no way in the world that the CD player would play "slow" or "flat" >> because of the nature of the beast. ... >> ...Pitch-shifting in the >> digital domain is a fairly ugly computational process, usually handled by >> high-speed DSP chips. > >This is wrong. Pitch shifting is easy. My first CD player was an >inexpensive one and it had a pitch adjustment control on it. It's my >guess that you can pitch shift just by changing the rate at which you >feed samples to the DtoA convertor. CD players already have circuitry >to adjust the rotation rate to keep the convertor FIFO happy, so I expect >that if you just change your sample clocking rate the slight change of >the disc rotation rate would occur automatically. Whoa. This is confusing two things: 1) Slow playback 2) Pitch shifting. They are different. 1) involves slowing down the whole system, and will slow down both the cadence and pitch of the signal. 2) involves doing information lossy signal processing of entirely non-trivial nature. It's very easy to imagine that the CD player has a bad crystal (doesn't matter why) that is 1% slow. 1% is easily heard as a pitch uncertainty. Of course, when tape machines are involved, one wonders if the mechanics of the tape machine aren't involved in the process, perhaps through drag problems, or machine to machine variations. Neither need involve the CD player. -- Question Authority *Mail to jj@alice.att.com or alice!jj Before *HASA, Atheist Curmudgeon Division IT *Copyright alice!jj 1990, all rights reserved, except Questions YOU! *transmission by USENET and like free facilities granted.
iann@tcom.stc.co.uk (Ian Newman) (06/05/90)
In article <55024@microsoft.UUCP> gordonl@microsoft.UUCP (Gordon LETWIN) writes: >> ...Pitch-shifting in the >> digital domain is a fairly ugly computational process, usually handled by >> high-speed DSP chips. > >This is wrong. Pitch shifting is easy. My first CD player was an >inexpensive one and it had a pitch adjustment control on it. It's my >guess that you can pitch shift just by changing the rate at which you >feed samples to the DtoA convertor. This is wrong. Pitch shifting by spinning a CD faster is impossible. If anythingit would only play the music faster, but at the same pitch. If your CD player did pitch shifting, it could only have done it at the analogue output stage, unless it had the appropriate DSP hardware in it, which I doubt. -- ------------------------------------------------------------- Ian Newman, STC Telecommunications Ltd., NMEC (Dept. 30770), Oakleigh Road South, New Southgate, London N11 1HB. <iann@tcom.stc.co.uk>
root@ninja.dell.com (Randy Davis) (06/06/90)
In article <6382.266ac585@umiami.miami.edu> chuck@umiami.miami.edu writes: | ..... I would rely on |the pitch of a CD over the pitch of a tape deck any day, especially since |the tape speed varies over the length of the tape, and the fact that the CD |player is (supposed to be) accurate to 1/44100 of a second. A nitpick: Tape speed DOES NOT vary over the length of the tape in a properly operating tape player, that's the purpose in life for the capstan and pinch roller. Tape speed is normally changable by adjusting the potentiometer on the pinch roller motor control board. On those decks, most of them, that use a single motor, this is not too hard to find. On those with multiple motors, one needs to find the motor that drives the capstan/pinch roller (normally the motor is connected to the pinch roller, and the capstan - the roller that is wide and covered with some friction material - is simply a passive component), and adjust the speed of this motor. In all the tape players I have seen, the take up reel is run at some high speed (higher than normal tape transport speed) that can easily pulled down to a lower speed by sufficient resistance. This resistance is supplied by the capstan/pinch roller regulating the speed - the take-up reel is trying to turn at a higher speed and keeps tension on the tape from the capstan/pinch roller to the take-up reel. At the same time, the supply reel is kept under a slight bit of reverse tension, in order to keep the tape taut from the supply reel to the capstan/pinch roller which contains, incidently, the stretch (no pun intended :-) that is in contact with the tape head. |I never thought this would be such a big thing... :-) Misinformation always proves to be a major discussion point.... Randy Davis UUCP: rjd@ninja.dell.com --
rich@island.uu.net (Rich Fanning) (06/06/90)
In article <6382.266ac585@umiami.miami.edu> chuck@umiami.miami.edu writes: >I would rely on >the pitch of a CD over the pitch of a tape deck any day, especially since >the tape speed varies over the length of the tape, and the fact that the CD >player is (supposed to be) accurate to 1/44100 of a second. The last statement is meaningless. The sample rate of CD is nominally 44.1 kHz, but the rate during playback, as many have said, is determined by the accuracy of the quartz crystal oscillator in the player itself. Most crystals are accurate to a fraction of a percent, but it wouldn't surprise me that some rock-bottom cheapo players might be off a lot more than more expensive ones. In any case, the phrase "accurate to 1/44100 of a second" doesn't mean anything. -- Rich Fanning {sun,ucbcad,uunet}island!rich
ken@cs.rochester.edu (Ken Yap) (06/06/90)
|>> ...Pitch-shifting in the |>> digital domain is a fairly ugly computational process, usually handled by |>> high-speed DSP chips. |> |>This is wrong. Pitch shifting is easy. My first CD player was an |>inexpensive one and it had a pitch adjustment control on it. It's my |>guess that you can pitch shift just by changing the rate at which you |>feed samples to the DtoA convertor. | |This is wrong. Pitch shifting by spinning a CD faster is impossible. If anythingit would only play the music faster, but at the same pitch. |If your CD player did pitch shifting, it could only have done it at the |analogue output stage, unless it had the appropriate DSP hardware in it, which |I doubt. Nope you're wrong. There was a project in Elektor to add pitch shifting to a particular line of CD players by altering the master clock, i.e. replace the crystal with an externally generated clock. So everything goes faster, including the drive motor, when you crank up the clock. Mind you, I'm not saying this is possible on every CD player. And I definitely think the original poster's CD player is spot on frequency-wise.
gcl@cbnewsj.att.com (george.c.layburn) (06/07/90)
> > Have you considered the possibility that the tape player(s) may be > running fast ? > > Check it CD against CD, and tell us, huh ? Or just check the time > elapsed count against a watch. > Ditto on the above, also make sure that neither machine has a pitch control being used. If the CD or tape speed is off there should hopefully be some way to adjust(calibrate) the speed but you will probably need some special equipment to do it. There used to be a disk called "The Digital Domain" that may still be available and it had several 1Khz test tones on it that you could use.
wiml@blake.acs.washington.edu (William Lewis) (06/07/90)
In article <89@rhum.tcom.stc.co.uk> iann@tcom.stc.co.uk (Ian Newman) writes: >In article <55024@microsoft.UUCP> gordonl@microsoft.UUCP (Gordon LETWIN) writes: >> >>This is wrong. Pitch shifting is easy. My first CD player was an >>inexpensive one and it had a pitch adjustment control on it. It's my >>guess that you can pitch shift just by changing the rate at which you >>feed samples to the DtoA convertor. > >This is wrong. Pitch shifting by spinning a CD faster is impossible. >If anythingit would only play the music faster, but at the same pitch. >If your CD player did pitch shifting, it could only have done it at the >analogue output stage, unless it had the appropriate DSP hardware in it, which >I doubt. You didn't read what he wrote. He said nothing about spinning the disk at a different rate. He was talking about clocking the D/A faster, which certainly WILL speed up the sound and increase the pitch, exactly like playing a record or tape at the wrong speed, as you would know if you had ever done it by accident. Anyway, I was under the impression that the disk speed is controlled by the FIFO length -- i.e., as the FIFO gets full, the disk slows; as it empties, the disk speeds up -- so the only "real" regulation at all is the rate at which the FIFO empties, i.e. the D/A's clock rate. >If anythingit would only play the music faster, but at the same pitch. I'd be surprised to find a simple way to do THAT without a DSP. -- JESUS SAVES | wiml@blake.acs.washington.edu Seattle, Washington but Clones 'R' Us makes backups! | 47 41' 15" N 122 42' 58" W
kline@ux1.cso.uiuc.edu (Charley Kline) (06/08/90)
1> This is wrong. Pitch shifting is easy. 2> This is wrong. Pitch shifting by spinning a CD faster is impossible. 3> You didn't read what he wrote. He said nothing about spinning the disk 4> Sorry Chuck, but that is not quite right. Does *ANYONE* know what they're talking about in this discussion??? Or is everyone just guessing? 0.5 :-) _____ Charley Kline, University of Illinois Computing Services c-kline@uiuc.edu Six weeks and counting down.