skip-free playback

[leeraff]

Can anyone explain exactly how this works? How well it works?

Does it make these devices (iMP's) truly skip-free? Or, really, just in an ideal world? Jogging? How much jarring, bumping can it REALLY take?

[Steelwolf]

Skip-free is a simple enough concept. There is a small buffer, usually a hard-wired volatile memory, like RAM in your computer. The device spins slightly faster than required to play the CD (audio or MP3) in real time. This allows it to read the CD and write to the buffer. The music is then played from the buffer. The buffer is kept full at all times.

In case of some jaring shock which causes the reading head to lose track, the music continues to play from the buffer. This gives enough time for the head to find its place again and begin reading. And since the CD spins slightly faster than required for real time playing, it can re-fill the buffer.

If the jaring continues too long and the head is unable to track properly for long enough, the buffer will eventually run out of information to play, at which time you will hear the skip.

When skip-free technology first came out, the buffers were small and 5-10 seconds was impressive. Now, audio CD-players can boast up to 30 seconds buffer and MP3 CDs can deliver even more (because the information is already compressed so more can fit in the buffer).

I hope that answers your question.

[Steelwolf]

I forgot to mention that the mechanical aspect of such players has also improved slightly, so they are not as sensitive to shocks. My first CD player had no buffer and even just putting it down on the table would jar it enough to skip.

My 2nd (and final) CD player had a 5 second buffer, but even with the buffer switched off (this option was provided to increase run time), it did not skip in many situations which would cause my first CD player to skip, such as the aforementioned "puttin down on the table".

Take it in context that my first CD player was bought around 1990-1991. My 2nd was bought in 1995 after the first unit was pinched by my brother and I started suffering withdrawal symptoms.

My first CD player had a special tray with shock absorbers for use in the car. My 2nd could handle much of a typical car ride placed on the passenger seat with the buffer switched off. With the buffer switched on, I never had any skips.

So to a degree, these newer CD players should be practically skip free, even for use in jogging. You'd have to be pretty mean to it, and for quite a long time, to get it to skip.

[leeraff]

Loving this site! 3 posts, 3 great answers. No bashing or tangents. (I'll soon stop mentioning this, but not sure the regulars know how lucky you are.)

So a brisk walk is a no-brainer. Jogging seems a little questionable from some (another post). But exercise walking should be fine?

[vinnie97]

How well the IMPs will do when jogging depends mainly on how the unit is situated. If you let it rest loosely and upright in your pocket with mp3s with a bitrate of at least 192 kbps, you're almost sure to empty the buffer (at least with the IMP-350 as I've personally experienced this) after no more than ~5 minutes. I haven't had the chance to confirm for myself but some say that placing it in a belt pack very much improves skip performance. Of course, the smaller the files, the less likely you are to experience skippage.

[HiredGun]

if you turn it on and start walking right away, it will skip. but you should let it play for a couple of minutes before moving it around a lot. when you do that, it virtually never skips. i had to sprint 3 blocks to catch the bus while the thing was playing and it didnt skip a beat.

[vinnie97]

What bitrate were yer files? It doesn't skip for a while as I jog until I reach a point (where the buffer no doubt empties) where the music catches up to the laser's position on the disc and annoying skips ensue. I might try again in the near future to give it a 3-minute warm-up, but I fear the same may happen when the buffer attempts to refill while jogging (of the 1-2 mile variety). I can't test atm anyhow as my battery died a while back and I haven't managed to find a replacement yet.

[jangell2]

I have some comments on skipping. I bought my iMP-550 several months ago and jogged with it in a waist belt. It did not skip for a month of jogging about 2-3 times a week. Then it started to skip.

Then I found that if I held it in my hands vertically it would not skip carried that way. I typically held it vertically. After doing that a while it started to skip that way too. Last night I went thru the manual and saw the option called "Shock Free." I had always thought any anti-skip features were always on.

So I ran with it today for 50 minutes with Shock Free on and carrying it in my hand vertically and not one skip. It worked perfectly. I am not a fast jogger but I think I have a heavy tread so I probably give it a good bump.

I should explain my jogging routine. I turn on the player, lay it flat on the ground, do my stretching for about 2 minutes, walk for 5 minutes, and then jog.

What is the 550 doing differently when Shock Free is on?

[bwoay]

Originally Posted by jangell2

What is the 550 doing differently when Shock Free is on?

it spins the CD a lot faster,
I don't know whether it does anything else besides that...
I'm more kurious about what it does when the Shock Free is OFF,
since I tried it with an audio CD,
and it does NOT spin the disk constantly,
so it's obvious, that even with the Shock Free turned off,
it still uses the buffer to pile the music in,
which is a bit strange for me.
I guess it should pass the buffer and spin the (audio) CD all the time,
when one is not using the anti-skip function.

[jangell2]

Well, I already had a waist-belt for my 550 so I tried that today for the first time with "Shock-Free" turned on. Previously it had skipped when using the waist-belt. I used the same routine I used as before except for the belt.

I ran for 50 minutes and not one skip! Alright.

[FlameGrilled]

How much can they take, the 'ShockFree' anti-shock system..??

Check this article out and you'll discover that it was (up until the iMP-550 came along), proven to be 'bombproof'.

God knows, if you'd experience the test first hand, you'd appreciate the sentiments as well as i do (i'm the author). Sadly, the rep that was good for the 250-400 decks didn't seem to be the case for the 550, as it let the side down badly.