G-Protection

[Sparda]

Does anybody know how long the G-Protection lasts for? Is it different on all units or the same. For the N910 it states that it lasts for 200 seconds but I think it lasts for a shorter time on my RH1. Because on some occasions I have experienced skipping. I suppose it could be that I shook it while it was reading so it couldn't load into the memory buffer and so it skipped? Just wonder why it skipped in such a short time period.

[Richard]

* Moved to appropriate sub-section of forum

[Karl Myer]

How does G-protection work on the MZ-RH1? A newly-inserted MD spins rapidly (vibration can be easily felt while holding the recorder) about 5-7 seconds, then, a few seconds into the track the vibration completely stops. I have held the recorder a long time, waiting for the vibration to start up again, but it never seems to -- the recorder is completely vibration- and noise-free the whole time it plays. My Discman CD player spins a disc a few seconds, then stops and reads from its solid state memory, then spins the disc again (to reload the memory, I'm assuming). It's easy to feel, and hear, its on-off cycles, and they are very regular. Does the RH1 operate some other way or is it just extremely smooth spinning a disc?

[eriktous]

I'm guessing it works the same way as your discman, but is, as you put it, extremely smooth spinning a disk. The rapid spinning you notice after inserting a new disk is probably needed to quickly fill up the play back buffer completely. After that it only has to refill the buffer partly, so it doesn't need to read in as big a burst.

[Karl Myer]

I think you are right. I have tried to feel the vibration by just holding the unit, without listening to speakers or through headphones, and in as quiet an enviornment as possible. A just-detectable vibration can be felt, which doesn't seem to cycle on and off. At times the only sure way to know it's vibrating is to press Stop/Cancel and feel it stop.

[cochra1]

I think you are right. I have tried to feel the vibration by just holding the unit, without listening to speakers or through headphones, and in as quiet an enviornment as possible. A just-detectable vibration can be felt, which doesn't seem to cycle on and off. At times the only sure way to know it's vibrating is to press Stop/Cancel and feel it stop.

Yeah, the NH1 - like all digital disc players - works the same way. Reads a bit from the disc, which is loaded into a buffer or memoray storage area, and this then feeds the DAC (digital-analogue-converter) which produces the analogue sound.

Because the disc can be read much faster than the DAC needs to convert to sound, it only needs to do this in dribs and drabs to keep the memory topped up as required. How often the disc needs to be read also depends on the bitrate of the files. Lower bitrates have less data per unit of sound so need to be read less during the course of any given listening period as the buffer is emptied more slowly and the DAC converts at a less strenuous rate, hence longer battery life at low bitrates.

I would guess that this intermittant disc spinning can't be physically heard or felt so much on the NH1 due to superb engineering.

[doomlordis]

There is no DAC (in the normal sense) in a NH1 , it has a digital amp which by definition takes care of the conversion.

[Sparda]

Also wonder what is the threshold before it needs to read again, say like 10, 15 seconds before the buffer runs out?

[greenmachine]

The buffer in (Hi-)MD units (and portable CD players) is in fact a small RAM (Random Access Memory), like the one in your computer. Every couple of seconds or minutes it is refilled with information from the disc. The audio that is sent to the headphone output is not directly read from the disc, but from the RAM. As long as there's new information in the RAM, there's no skipping, no matter how hard you shake the unit since there are no moving/mechanical parts in a RAM.

Initially (when starting to play back a disc), the RAM is filled completely with data from the disc, which takes a couple of seconds. After that, the disc mechanism is idle until the RAM reached a certain degree of emptiness*. It wouldn't be very smart to refill the RAM only when completely emptied since the unit is susceptible to shock in the disc reading process, which would cause immediate skipping/dropouts. If the buffer is refilled before completely empty, there is some buffer left in case the disc can't be read immediately (shock).

If the unit is under constant serious shock, the RAM can't be rewritten, which will bring playback to a halt eventually. If the shock occurs periodically, there's usually time for the buffer to be rewritten before it runs empty.

The RAM has a certain size. The lower the bitrate of the audio (less information per time period), the less often the RAM needs to be refilled. The lower the bitrate, the more efficient the anti-skip mechanism will work for several reasons:

- The speed of the disc drive is limited, it takes longer to read a 30 second PCM file (1411kbps**) than it would take to read a 30 second Hi-LP file (64kbps).

- It is sufficient to refill the RAM at a later stage (higher degree of emptiness) with a low bitrate file. A certain buffer time will take less space on the fixed-size RAM. Information needs to read less often from the disc.

On my NH700 and a 1GB disc, the read/refill process takes about 8 seconds. In PCM mode, the disc mechanism is idle for about 30 seconds before the next refill process takes place. In Hi-SP mode slightly more than 3 minutes, in Hi-LP mode just over 14 minutes. I suspect the RAM to be 8MB in size since a 14 minute Hi-LP (64kbps) file would be roughly 7 MB large and there must be still some buffer left (as explained above).

*empty = no new/relevant information to read

**kbps = kilobits per second

[Karl Myer]

It is possible my content was 64kbps (an audiobook) and although I held the RH-1 a long time trying to feel the disc spinning I didn't hold it 14 minutes.

I'm currently listening to tracks originally made on either my 1993 or 2000 model-year recorders that I transferred a couple days ago into My Library in Sonic Stage, then converted to PCM, then transferred onto a 1GB Hi-MD in PCM. I plan to listen to it tonight just to make sure everything transferred correctly before I erase the original disc and reformat it as a blank Hi-MD.

I will try again to feel the RH-1 cycle on and off, this time with the PCM recording. Thank you for the very nice explanation.

[greenmachine]

I don't think the very gentle spinning of the disc causes enough vibrations so that it can be easily felt, but the motor noise can certainly be heard in a quiet environment. It would be interesting to see if the RH1 behaves the same way, or if they maybe increased the buffer size.

Edited March 2, 2007 by greenmachine

[Karl Myer]

My tests:

Note: I am holding MZ-RH1 still, so no shocks.

Note: Discs seem to be spun at one of three intensity levels: (1) very soft (2) moderate (3) intense.

--- Playing a Sony 1GB Hi-MD recorded in PCM, disc spins 8 seconds then does not spin for 30 seconds. This sequence is very regular -- I timed it through ten cycles. Spinning is very soft -- so soft it is hard to feel -- even when disc is first loaded.

--- Playing a legacy Sony 60min MD, reformatted to Hi-MD, recorded at 64 kbps, disc spins 8 seconds then does not spin for the next 16 minutes. I don't know whether this sequence is regular since I only timed it through one cycle. Disc spins intensely when first loaded then moderately when it next spins 16 minutes later.

--- Playing a Sony 1GB Hi-MD recorded at 64 kbps, disc spins 8 seconds then does not spin for the next 18 minutes. I don't know whether this sequence is regular since I only timed it through one cycle. Spinning is very soft -- so soft it is hard to feel -- even when disc is first loaded.

--- Playing a legacy Sony 60min MD, reformatted to Hi-MD, recorded in PCM, disc spins 18 (yes 18, not 8) seconds then does not spin for 30 seconds. This sequence is very regular -- I timed it through ten cycles. Disc spins intensely when first loaded then moderately whenever it again spins at the 30-second intervals. But whether moderate or intense it always spins 18 seconds.

One surprising conclusion is the 1GB MD seems to be a refinement over previous MD's in that the disc is only ever spun at the very soft level of intensity. I don't know if this is also true of 60-, 74-, and 80min Hi-MD's because I don't own any, but if not I think I would only buy 1GB discs. In any case, my reformatted-to-Hi-MD legacy 60min disc was never spun by the RH1 at the soft level.

By the way, am I using "legacy" correctly? I first encountered the word when first viewing this website a month ago and have been unsuccessful verifying its meaning. I use it for 'minidiscs manufactured before the Net-MD era.' I would be interested to know its origins.

[greenmachine]

If you think about it, it seems quite logical that on standard MDs the read intervals need to be longer or at a higher speed or both: There is less information to be read/written, but spread onto the same physical space, or in other words, the read/write mechanism must work its way through a whole disc in less time.

[Sparky191]

There is no DAC (in the normal sense) in a NH1 , it has a digital amp which by definition takes care of the conversion.

What do you mean?

[Sparda]

What do you mean?

Yeah, I didn't quite get that too. Isn't the DAC where it goes from digital signal to analogue then straight to headphone/line-out? And then before the DAC there would be a decoder/processing unit?

[Sparky191]

If theres was a digtial/optical out/in might bypass a ADC/DAC on the unit it self. AFAIK Theres always a DAC or ADC somewhere before it gets to your ears.

http://en.wikipedia.org/wiki/Digital-to-analog_converter

http://en.wikipedia.org/wiki/Analog-to-digital_converter

Edited May 21, 2007 by Sparky191

[doomlordis]

If theres was a digtial/optical out/in might bypass a ADC/DAC on the unit it self. AFAIK Theres always a DAC or ADC somewhere before it gets to your ears.

http://en.wikipedia.org/wiki/Digital-to-analog_converter

http://en.wikipedia.org/wiki/Analog-to-digital_converter

Sorry for very late reply but just seen your replys today, in respect to DAcs or lack of in digital amplifiers , In the analog amp signal chain PCM data from the DSP would get converted into an analog signal by the DAC, and then be amplified.

In digital amps the DSP receives the digital source signal , processes it and outputs it as PCM , there will then be a PWM processor that will covert the PCM into PWM format, this is passed to the Powerstage, this converts the 3.3 volt PWM signal up to around 20 - 40 volts and usually passes it through a low pass filter at this point it is in the analogue domain.

So no DAC as such.

Edited January 10, 2008 by doomlordis