What makes an audio CD stutter?

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ThomasHenry
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What makes an audio CD stutter?

Post by ThomasHenry » Sun Sep 19, 2004 8:22 pm

Hi gang,<p>I'm trying to add to my knowledge of the audio CD technology. The following real-world problem has arisen; I'd be glad to hear your comments.<p>In short: what is going on when an audio CD skips or stutters, repeating passages and so forth? Is it software or is it hardware, is it solid-state or is it electrical (i.e., motors or electromechanical devices), or is it the medium itself?<p>I ask because I've got a huge collection of old radio plays which I've burned to CD. I love to listen to these at night while falling asleep. Over the past two years I've tried three brands of CD/clock/radios. Most recently I tried a GE unit which has a beautiful clock display, an excellent dual-alarm and a nap feature. It really is a well thought out design, ergonomically speaking. But, I've gone through three of these so far with varying results. The first played perfectly, but then the display light burned out after a week. Replacing it, the second one stuttered constantly. Again, replacing it, the third one stutters once or twice a disk, and will need to be replaced yet again.<p>So, any idea what's going on? The unit claims to be CD-R compatible, and screws up on my discs, which play just fine on either the computer CD unit, my "walkman" type portable ($15!) or my big home stereo player.<p>My curiosity is up.<p>Best wishes,<p>Thomas Henry

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Chris Smith
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Re: What makes an audio CD stutter?

Post by Chris Smith » Sun Sep 19, 2004 8:58 pm

It’s the buffer, the digital buffer. <p>A.K.A. Ram or Rom involved in the playback. <p> If you have a large buffer, then your music stream is played well in advance of what your system is reading, processed and playing back while reading many seconds behind, and any skip is ignored in time and re-fed into the buffer well before you can hear its mistakes.<p> If the buffer is tiny, then any skip will follow shortly before the system can recover and feed back in the proper digital string to correct it, and thus you hear the error.<p>When using a computer with other programs running, the error occurs because of steering in the IRQ and Resources available.<p> Like a traffic light, the computer steers available resources not acording to your wishes, but acording to its necessity, and thus drop out is not priority based on what you want, but how the computer best handles numbers or bits with out crashing.

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haklesup
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Re: What makes an audio CD stutter?

Post by haklesup » Mon Sep 20, 2004 2:51 pm

Assuming your disk is clean and free of obvious scratches.<p>The buffer certainly has a lot to do with how well a drive can compensate for gaps in the serial data stream coming from the pickup head off the disk. This used to be a big selling feature on CD players years ago but I think all newer drives have ample buffer size. In any case, they don't make a big deal about it (anti skip buffer) in marketing specs anymore.<p>Even the biggest buffer cannot compensate for gross errors in reading the disk. Long gaps cause the drive to go back to the last place it had good data and try again or simply pick up at a predicted spot on the disk (repeats or skips). Except dirt and scratches, these errors can be caused by a whole bunch of things that you ultimately cannot adjust (like focus, tracking, disk wobble and more) It simply comes back to the quality of the drive manufacture.<p>Since you tried three of the same model with poor results, its time to move on. If you have money to burn (who does) the Bose Wave radio looks like a quality piece (though I do not have one).<p>Does anyone make an alarm clock / MP3 jukebox? That would be a cool solution. I bet we'll see that in the next year or two.

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Re: What makes an audio CD stutter?

Post by Mike » Mon Sep 20, 2004 3:17 pm

I don't know about the bose, their products have never impressed me, especially the sound quality, very poor for the price.<p>I'm sure somebody already makes an MP3/CD player alarm clock. It can't be that hard to do.

ThomasHenry
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Re: What makes an audio CD stutter?

Post by ThomasHenry » Mon Sep 20, 2004 5:12 pm

Thanks to all for the explanations.<p>I too don't think a limited buffer is the problem, since the first unit (same model) worked well. In other words, it doesn't seem to be an inherent design issue but something that varies from unit to unit.<p>My curiosity is up as to what is going on, just in the scientific spirit of the thing. So I'm keeping track of something I noticed yesterday: so far it seems that commercial discs don't stutter ever, but CD-R's do. The trouble is, the stuttering is so infrequent, I can't claim a pattern yet for sure, but it sort of looks like it may turn out that way.<p>I will no doubt move on to another brand, but I figured I'd try to understand the problem a bit more first. I might as well learn something in the process...<p>Thanks again,<p>Thomas Henry

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Re: What makes an audio CD stutter?

Post by ThomasHenry » Sat Sep 25, 2004 10:32 am

Well, the results are in. I ended up trying a grand total of 5 of these GE CD/Clock Radios. The first one played great, but the display burned out in a week. The remaining four skipped and stuttered all over the place.<p>What I observed: all could play commercial CDs without a problem, but only one could play CD-R's reliably (even though the package indicated CD-R capability). Note that even my other cheapo $18 unit could play a CD-R, but as soon as I tried the same one on the GE unit, it skipped.<p>What do you think, a lousy laser design? It sort of seems like the GE can't pick up the patterns as reliably as my cheapo (and other) units.<p>Anyway, I'm done with that model!

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Chris Smith
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Re: What makes an audio CD stutter?

Post by Chris Smith » Sat Sep 25, 2004 11:28 am

Copy the CDR to your hard drive and if the music doesn’t skip, then you have a lousy tracking system in your unit rather than the laser it self. <p>Its supposed to be a linear tracking system, but its controlled by a bit stream also. How the cradle tracks and follows is everything.<p> Its like the old days of tone arms and needles, the heavier or too light it was the more likely it was to skip. Then they went to linear tracking and solved most of the problems.

ThomasHenry
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Re: What makes an audio CD stutter?

Post by ThomasHenry » Sat Sep 25, 2004 2:36 pm

Thanks. As I mentioned, any of these CD-R's play just fine on every other unit I have (three different units from portable to component system). The fact that the GE only has trouble with them, but NOT with commercial CD's suggests to me it's optical rather than mechanical difficulties. I'm guessing that the tracking, spin, and other mechanical aspects should remain the same whether a commercial CD or CD-R is being played. But certainly the optical qualities could vary.<p>Does that sound right?<p>And, oh, of course the CD-R's play well on my computer, too.

Enzo
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Re: What makes an audio CD stutter?

Post by Enzo » Sun Sep 26, 2004 5:59 pm

If the thing skipped on CDs in general we could hypothesize about things like dirty optics, stickly rails , and dirt in the gears. When I encounter CD problems in my work, I first clean the lens - that is most of the trouble. Then a quick wipe and relube of the rails the laser unti slides on. If the lube dries out it gets sticky. And the little gears that drive the sled back and forth on those rails need to be clear. a cat hair or speck of dirt in the gears can impede the works.<p>BUT<p>Yours works fine on commercial stamped CDs, so none of that is the case. There is nothing wrong with your player, it is doing what it was s=designed to do. Your burned CDs are not up to the same standard as the radio. They work in their own burner and similar situations, but they are marginal for this application.<p>I don't know if your burner has any adjustable parameters, but at the very least, burn some CDs on other systems than your own - and make sure they are diffrent models of equipment, not just soimeone else's same thing - and see if they play.

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