Subject:WOW, --EQing reducees file size ??

Posted by: fosko

Date:11/5/2002 9:37:37 PM

OK, I'm no audio engineer , and after I think about it .. it makes sense, but I'm still surprised.

Was reading an article in Sept 2001 Electronic Musician about preparing files for streaming audio. One suggestion was to cut frequencies below 60hz and above 12 khz since those proabbly wouldn't be heard in lower end systems. Well my files is voice (a sermon/lecture) and it's about47 minutes. I decided to save the files and compare.
I also went a bit further on cutting frequencies since the fidelity wasn't as important.

My file size went from 1.99gigs to about 500 megs. I guess it makes sense. Cut frequencies..cut data ???

I'm also goingto convert from stero to mono. see if that does anything.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: Geoff_Wood

Date:11/6/2002 12:59:31 AM

I assume you are talking about a file that is perceptually encoded for streaming ?

There should be no change in size for a wav file (linear PCM).

geoff

Subject:RE: WOW, --EQing reducees file size ??

Reply by: Chienworks

Date:11/6/2002 10:05:44 AM

1.99GB for 47 minutes? That's an enormous file! Even recording 96KHz stereo 24bit should only have been about 1.5GB. What file types are these? What number of channels, sample rate, bit depth, etc? The 500MB file is probably standard CD quality 44.1KHz stereo 16 bit.

When you get your 47 minutes ready for streaming, you should probably be looking at a file that is in the 10 to 15MB range, depending on what bitrate sounds acceptable to you.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: fosko

Date:11/6/2002 2:57:21 PM

well, it was recorded from tape..through deta 1010 into VEGAS. Was recorded at a standard 44 -16 bit. I thought 1.99 gigs was big too. I tweaked a bit...killed some frequencies, changed to mono, and then changed resolution to22.5. Broughtthe file size waaay down ( I'm at work now so can't give you actual numbers(.

I saved each version to compare. then....I rendered each as .wma. What is surprising is.. I didnt get the same "savings" when I rendered. The new edited files was only very slightly smaller than the original when both were changed to .wma.

Does me theroy that cutting unheard frequencies cut file size hold water ??

Subject:RE: WOW, --EQing reducees file size ??

Reply by: Chienworks

Date:11/6/2002 4:03:24 PM

Well, that's actually almost entirely UN-true. The size of the compressed output file is defined by the bitrate used when compressing it. No matter how many channels, sample rate, bit depth, or whatever the original file has, when you save it to 64Kbps WMA, it will be 64Kbps. The only things that affect the file size are the encoding bit rate multiplied by the length of the recording.

However, i think the point that article was getting at was that if you eliminate unnecessary parts of the recording (in this case frequencies outside the main vocal range), you can compress to a lower bitrate and retain acceptable quality better than if you didn't elimate the unnecessary parts. If there's less information in the signal, then fewer bits are needed to encode it successfully. But, in order to get a smaller output file, you'll have to save it with a lower bitrate.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: Rednroll

Date:11/6/2002 4:05:09 PM

You should get approximately 10Meg per 1 minute of 16bit 44.1Khz stereo .Wav file. So your 47 minute recording should only be about 470 Megs. Something is definitely wrong. Are you sure you're recording as a 16 bit 44.1Khz .WAV? Also you can usually expect a compression of 10 to 1 when rendering to a 128 Kbs .MP3...so even at this compression you would expect only a file size of 47Megs or 1 meg per minute.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: fosko

Date:11/6/2002 7:41:40 PM

THAnks Chein, that clears somethings up :-)

Yep I just converted another in the series from tape to Digital.
44.100 hz
16 bit
stero
Here's the thing...
I left my recorder on while I was at work. The original file was 3:22:55 however only the first 1:02:47 had data/sound. THAT file was over 2 gigs.

I then trimmed the slience and got the file down to1:02:47 at 638 megs.

I see size does matter....not content.

and thanks to Cheins expalnation I now realize 64 kbp is Kilobites per second (DUH).. so I could conpress a solo voice or a symphony..it wouldn't matter.

And Red.. thanks, your calculation came out right on the money..

The one thing I missed becoming a music major was not taking anymore physics classes.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: fosko

Date:11/6/2002 7:56:32 PM

One other side note..
I did notice that by going from stero to mono I cut files size in half. also by resampling down from 44.0 hz to 22.5. I cut it in half again. But as stated before.. all of those files were the same saixe when encode to .wma

thought this might help someone else out later who's a novice like me.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: Rednroll

Date:11/7/2002 9:51:27 AM

If you're converting from stereo to mono, then save yourself some headache and drive space. When you record into sound Forge you can record as a Mono file instead of a stereo file, which will automatically cut your file size in half and then double your available recording time.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: rraud

Date:11/7/2002 7:04:06 PM

Red & Chien are absolutly correct as usual.
May I add, if your final product is going to be an MP3, the MP3 file size will be about the same... stereo OR mono.

Subject:RE: WOW, --EQing reducees file size ??

Reply by: fosko

Date:11/8/2002 12:09:47 AM

THanks for the tips...really helped.
I figuered since I'm streaming..andit's voice, I'd stick with the lesser quality, but smaller file size of Window Media player and REAL Media.

Unless of course you guys have any other suggestions ;-)