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What is "compressed ROM"?


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This may be a dumb question, but when ROMpler manufacturers talk about "compressed ROM", what does it mean? I've never been able to get a definitive answer to this. You know, typical ROM-speak, like from Yamaha or Roland or Kurzweil: "The new XDF78000 contains 64MB* of ROM", and then when you read the asterisk at the bottom of the page it says "(When converted to 16-bit linear format)" or something like that.

 

First off, is it a lossless or lossy form of compression? Lossless being like PKZip, and lossy being like MP3 or Minidisc. They're not talking about audio compression where the dynamics are compressed, are they?

 

If it's 64MB when converted to linear format, does that mean that they're actually storing that 64MB on 32MB ROM chips, for example?

 

 

This message has been edited by guestuser@guestuser.com on 03-16-2001 at 10:03 AM

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It's a way for manufacturers to keep the cost of synths, or anything that uses samples, down. They typically use their own, proprietary, algorithm to compress the samples - supposedly it's lossless. My guess is that it works pretty well, because if they're working with a 'known quantity' (they know what samples will be used and what the exact 1/0 data looks like and it's the same on every ROM...), they can do a really good job on the compression algorithm.
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Correct. In fact one interesting note is that Kurzweil always documents the amount of data, based on the amount of physical space used on a chip. I think that we're the only company that does this. So people are easily thrown when they read that the K2600 comes standard with only 12MB of ROM.

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Originally posted by Mike Martin:

Correct. In fact one interesting note is that Kurzweil always documents the amount of data, based on the amount of physical space used on a chip. I think that we're the only company that does this. So people are easily thrown when they read that the K2600 comes standard with only 12MB of ROM.

 

Why not also list the amount of ROM in its "uncompressed" form?

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I second that! I didn't think that the Kurzweil could use compression at all! I would be very intersted to know what its "16bit linear format rating is".

 

Both Roland and Yamaha are having serious problems with this stuff.. I have a feeling that the SRX boards have basically 32megs of ROM. As for the claimed 85 Megs in the Motif, I doubt if that's more than 32 or 48 megs realistically. I'm pretty sure that the Korg Triton's rom is uncompressed, mostly because I've never seen that little asterisk next to their ads. Plus I don't have the faith that they could actually come up with a decent compression scheme, lol.

 

The funniest example, I think, is with the Clavia ddrum4, which claims to have the best sounds around because it has the most memory due to a super advanced lossless compression scheme, which they describe like this:

 

"The new storing format is based on algorithms for analyzing redundancy in percussive sound with respect to the important transient response of a typical percussive instrument. Thanks to this effective storing format, the memory capacity is multiplied 4-6 times depending on the types of samples. "

 

They then claim that the whopping 8 Megabytes of Flash ROM in the unit stores an "equivalent to 32 to 48 MB uncompressed".

 

So what?

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I guess I should hold off on talking about things that I'm not 100% certain about. Plus I'm exhausted and haven't slept much. I'll see if I can get some better comfirmation about this during daytime hours after I've had some sleep.

 

 

 

This message has been edited by Mike Martin on 03-15-2001 at 11:02 PM

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Originally posted by Steve44:

I'm pretty sure that the Korg Triton's rom is uncompressed, mostly because I've never seen that little asterisk next to their ads. Plus I don't have the faith that they could actually come up with a decent compression scheme, lol.

 

Gee, you have more faith in them than me. I would think that all the ROMpler manufacturers compress their data to make it harder to rip off, as well as to save money on ROM chips. I'm pretty sure I read somewhere that the Triton's ROM is compressed just like everybody else. Can't remeber where though. Maybe that's what "Sound processed with Infinity" means.

 

 

 

 

This message has been edited by guestuser@guestuser.com on 03-15-2001 at 11:47 PM

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Originally posted by Mike Martin:

Well, I stand corrected. I was having a conversation with one of our engineers and asking him why we did it this way...from a marketing perspective. Aparently its not compressed after all.

 

Hate to tell you this, but according to my K2000R's manual, it's ROM is compressed (see page 6-24 re natural amplitude envelope. And according to the K2600's manual, it's the same way - see page 6-35 re natural amplitude envelope. Your engineer must be a new guy ;-)

 

 

This message has been edited by guestuser@guestuser.com on 03-15-2001 at 11:16 PM

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Korg's always just said the Triton has 32 Megs of ROM. It never said anythign about compression. But then again, when they said that they were releasing almost all the waves of the Triton and the first three expansion boards (32+48=80 Megs) for the OASYS they quoted 145 Megabytes. So I guess they probably use 2 to 1 compression after all.. but that would mean that the Triton's ROM is really 64 megs.. and that doesn't sound right at all.. so maybe I'm completely off base.

 

Where's the Korg version of Mike Martin when you need him? Wait.. I have his card somewhere... Bobby Nelson. Maybe I can convince him to join up on this forum http://www.musicplayer.com/ubb/smile.gif

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Hate to tell you this, but according to my K2000R's manual, it's ROM is compressed (see page 6-24 re natural amplitude envelope. And according to the K2600's manual, it's the same way - see page 6-35 re natural amplitude envelope.

 

If memory serves, Kurweil's method of compressing that you are speaking about is called amplitude scaling, and I believe they are the only ones that do it that way. There are two other methods that I know of:

 

Sample skipping - just what it sounds like...up to three samples get skipped, so one out of every four gets used.

 

Delta-sigma, which (if I understand it correctly) pays more attention to the change between values than the values themselves.

 

As I understand it, sample skipping is the preferred method of data compression among synth manufacturers. When a synth manufacturer says that their 16MB waveform would actually be 64MB if uncompressed, I believe they're saying that they're skipping three out of every four samples.

 

I'm hardly an expert in this field - anyone who can enlighten us further is encouraged to do so...

 

dB

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I would think that all the ROMpler manufacturers compress their data to make it harder to rip off, as well as to save money on ROM chips.

 

Not all...

 

Alesis does not compress their sound ROMs. I believe they are the only exception to the rule, though.

 

dB

:snax:

 

:keys:==> David Bryce Music • Funky Young Monks <==:rawk:

 

Professional Affiliations: Royer LabsMusic Player Network

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Interesting. So, that would be a lossy compression scheme, then?

 

Like I've said, I am far from being an expert on data compression; but, from my limited understanding, by definition anything that loses any data is lossy. The so-called lossless methods literally lose no data at all.

 

Once again, any clarification from anyone who knows better is not only welcome, but encouraged...

 

dB

:snax:

 

:keys:==> David Bryce Music • Funky Young Monks <==:rawk:

 

Professional Affiliations: Royer LabsMusic Player Network

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