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Topic: Zipping Wav Files |
Roy Thomson
From:
Wolfville, Nova Scotia,Canada
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Posted 12 May 2000 6:20 am |
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I note that when "zipping" files the rate of compression varies. A recent file I zipped compressed only 11%. Others have been as high as 66%.
Can anyone shed some light on this?
In essence I would like to be able to maintain a good quality to digital files when converting to wavs and compressing while sending them as email attachments that will not take too long to download on the receivers end.
Thanks for any attention
Roy T. |
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Jack Stoner
From:
Kansas City, MO
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Posted 12 May 2000 9:18 am
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| The type of file will determine how much compression will occur. If the file is already in a format that compresses data (e.g. a jpg graphic) then using a zip program may not reduce it that much further. |
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Jeff Agnew
From:
Dallas, TX
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Posted 12 May 2000 9:49 am
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It's the content of the file which determines its compressability. Zip works by removing repeating information with a single marker. In a text file, for a loosely related example, if the document contained many instances of the word "the" then Zip might replace it with a unique single character. That would save several bytes in each instance.
The second part of your question is, I think, making an incorrect assumption. You won't lose any quality from the original .wav file if you use PKZIP to compress it. Zip is a lossless compression format, meaning that an expanded file is an exact copy of the original.
As Jack mentioned, JPEG is a lossy format. It applies an algorithm to determine which information can be discarded. In fact, every time you save a .jpg file you are re-compressing it. That's why pictures which have been compressed too much look lousy; much of the original information has been thrown away.
With zipped .wav files, you can't control the amount of compression anyway so you needn't worry. MP3, however, is a lossy format like JPEG. There is a definite quality loss as compression increases. The higher the compression level, the smaller the file and the poorer the audio quality.
Finally, you can rezip a zipped .wav file, but you won't notice an additional savings. If file size is your ultimate consideration, you'll need to look at a lossy format such as MP3 or Shockwave.
All probably more than you wanted to know...
Regards,
Jeff |
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Roy Thomson
From:
Wolfville, Nova Scotia,Canada
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Posted 12 May 2000 10:23 am
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OK but what about the....
44,100 Hz 16 bit stereo/mono
22,050 " 31KB/S
11025
8000 """ etc. etc.
Don't these choice of recording settings govern quality
of wav file? Don't they compress at different rates?
I know they upload and download at different rates.
Roy T.
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Jim Cohen
From:
Philadelphia, PA
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Posted 12 May 2000 2:32 pm
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| Somebody here turned me on to a program called "Easy CD-DA Extractor" that makes wav files for the Windows Media Player (*.wma files) They are much smaller than mp3 files (like one-tenth!) and can be emailed much more easily. I can't remember the link where I downloaded it, but if you do a search for it, I'm sure it will come up. |
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Bobby Lee
From:
Cloverdale, California, USA
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Posted 13 May 2000 10:47 am
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Roy, those WAV file settings have nothing to do with compression. They actually control the amount of data that is captured.
The 44kHz setting is the sampling rate for CDs. This basically gives you enough data to cover the full range of human hearing. The rule for digital data is that the sampling frequency has to be at least twice that of the highest frequency of the data. We can hear up to about 20kHz, so they fixed the sample rate for CDs just above 40kHz.
When you cut it in half (22Hz), you lose data at the very high end of the frequency spectrum (everything higher than 11kHz). But since the sampling rate is half, the amount of data is half and the file size is half.
So, while it may appear that you have "compressed" the file, you haven't really. You've just thrown away half of the data, and told the WAV player to use one sample instead of two for that fraction of a second. So it sounds "duller", like it would if you took the highest slider of a 1-octave graphic equalizer and pulled it all the way down.
At 11kHz sampling, it's like taking the top two sliders of that equalizer and pulling them down. You are capturing no data in that range, and your file size is 1/4 that of a "CD quality" file. The tradeoff is that you've lost another octave of sound off the high end. Nothing over 5,500 Hz is audible. Make sense?
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 Bobby Lee quasar@b0b.com gigs CDs
Sierra Session S-12 (E9), Speedy West D-10 (E9, D6),
Sierra S-8 Laptop (D13), Fender Stringmaster D-8 (D13, A6) |
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Bill Nauman
From:
Cresco,Pa,USA
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Posted 16 May 2000 10:09 am
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I use the CD DA easy extractor program and compress raw wavs down to about 200k in WMA format...however if you are planning to eventually burn on to CD you want the raw wav at its best quality WMA works fine for email purposes.. Bill in Vegas
get it from Download.com ...search CD DA Easy Extractor program
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