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Is compression used in CDs?
Mr. Mulder
post Jul 11 2002, 09:59
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QUOTE
Originally posted by godzilla525
RightMark's test tones are way too short.  They don't even use a sweep, but more of a weird buzz. It would also be tricky to get it timed just right.

I wish I knew of any open-source or free software tools for making sine sweeps and such.  Hopefully someone else does. ???


Frequency Master Generator 0.93: http://www.hot.ee/smpman/fmg/fmg093.zip

"Frequency master generator" is an universal tool which can be used to produce
different frequency sequences and sounds in special and convenient way.

Actually, it is a translator, which translates your commands and
synthesizes them in a given order.

With this program you will able to produce ANY sounds easely even "fantastic"
and "mystic" ones never heared before!

Because of output is standard PCM data .WAV file you can use your new sounds
as samples and instruments in any sound-editor and/or music composing program.

This program is also very usefull for people who are testing different audio
devices and perceptual audio compressing algorithms ( like MPEG coders ).
They will be able to generate exact and special signals with this frequency
generator.


--------------------
"The R.I.A.A. is out there"
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westgroveg
post Jul 11 2002, 10:05
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So then if vinyl records are not compressed they should sound better than Compact disc audio with the right record player?.
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JonPike
post Jul 11 2002, 10:40
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I'll have to go looking thru some bookmarks..

In the speaker and audio testing realm, there is freeware and demoware out there that might give you a deeper analysis. They might even work under these conditions, though it's still a wierd setup, unlike what they're designed to test.

The Cool Edit editor (and more) program, in case you didn't know about it, is available as a free demo, (slightly crippled and "hassleware") that can both generate tone sweeps as well as do nice spectral analysis on the results. www.syntrillium.com

We had a thread going a while back on sound cards, where we got rather into testing with Cool Edit and Right Mark..

If you try this, one thing we discovered was most cards do better at 48Khz, at least the Live and Audigy sure do better due to internal conversion. (or lack of, when you run at 48Khz) 44.1Khz, you could have HF artifacts above 10Khz with that 20-20Khz sweep, but they'll be caused by the sound card!

So, generate a 48Khz wav for your sweep, it'll be pretty clean.

Just tried this again.. found that most of the noisyness is caused during the playing back of the wav file. That won't happen when the CD player is playing back. (unless it really is a noisy device!) But if you want clean "control" files, you could play back those files.. Also know, the freq response is much flatter, and the cards have lower distortion and noise when run in their native 48Khz..

Happy testing..

Jon
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KikeG
post Jul 11 2002, 14:18
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QUOTE
Originally posted by bryant
And when 24-bit data is compressed to 16-bit, the final step is truncation, even if there are noise shaping and dithering operations performed first to lessen the audible impact.


Well, dithering is considered to be a different thing from truncation, although it is true that at last, and in the strict meaning of the word, you have to do truncation.

But the purpose of dither is to totally eliminate the digital distortion that occurs when you do plain truncation, be it doing bit-depth reduction or a/d conversion. Also, to be able to capture and reproduce signals that are below the 16 bit LSB, again, without distortion (just noise).

Note that dithering should be an inherent part of any properly designed analog to digital conversion process, or bit depth reduction process.
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KikeG
post Jul 11 2002, 14:27
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QUOTE
Originally posted by westgroveg
So then if vinyl records are not compressed they should sound better than Compact disc audio with the right record player?.


Vinyl records have another form of compression, which is somehow "dynamics" compression at low frequencies (RIAA eq.) , in order to overcome the mechanical problems at the playing stage.

Note that the digital "compression" we are talking about at this thread, translates from a technical point of view into SNR or dynamic range. Note too that the dynamic range of 16 bit cd-audio (~96 dB) is far, far better than the dynamic range or SNR of vinyl (lots of background noise).
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godzilla525
post Jul 11 2002, 18:32
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Thanks for the links. smile.gif


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godzilla525
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westgroveg
post Jul 12 2002, 08:33
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QUOTE
Originally posted by KikeG


Vinyl records have another form of compression, which is somehow "dynamics" compression at low frequencies (RIAA eq.) , in order to overcome the mechanical problems at the playing stage.

Note that the digital "compression" we are talking about at this thread, translates from a technical point of view into SNR or dynamic range. Note too that the dynamic range of 16 bit cd-audio (~96 dB) is far, far better than the dynamic range or SNR of vinyl (lots of background noise).


Thanks for clearing that up Kiky.
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