[Ham-Computers] RE: cd conversion

[Hsu, Aaron (NBC Universal)]

Hi Jerry,

Sorry to hear your having such a hard time doing what really should be a simple task - making a good copy of a cassette!  But, unfortunately, there are *MANY* different audio formats on computers and knowing which one to use for what purpose can be a mind-puzzling experience.  Just for kicks, here's a list of common PC "audio" formats (file exensions):  WAV, MP3, MP4, M4A, AAC, OGG, AIFF, WMA, FLAC, APE (Monkey's Audio), RA (Real), and others.  And, with each of these formats, there are different quality settings such as bitrate, bit-depth, and even complexity level.

WAV is the "original" digital audio format as it's just a simple digital representation of the original audio stream.  Essentially, it's the digital output of an ADC (Analog to Digital Converter) written directly to a file.  Analog in, Digital out...plain and simple.  In order to properly "sample" audio, the ADC needs to be configured to capture the full details of the audio.  The Nyquist theorum states that an analog signal needs to be sampled at a minimum of twice the highest frequency being sampled.  So, with audio ranging 20 to 20KHz, the creators of the Compact Disc (CD) format chose 44.1KHz as the sampling frequency (capturing up to 22.05KHz).  The dynamic range was set to 16-bit depth resulting in a 96dB dynamic range - much higher than cassette or vinyl, but often considered "average" these days.  So, 44.1KHz @ 16-bit became known as the "Red Book" standard.  There's actually much more to the "Red Book" standard, but 44.1KHz and 16-bit depth are all we need to know for now.

Now, on a computer, you can capture WAV files using just about any sample-rate or bit-depth you want (with the resulting increase/decrease of frequency and dynamic range).  But, if you want to create an "Audio CD" that will playback on a CD player, then the CD must be written in Red Book standard format - 44KHz @ 16-bit sampling.  Most CD "burning" programs have an option or wizard for the "CD-Audio" format (as opposed to a "data" CD).  If you select this, then the resulting CD you burn should be in Red Book format.  The program does this by examing the audio files you've put into the "compiliation" and converting it to the 44.1KHz at 16-bit sample level prior to actually buring it onto the CD.  Just realize that the 44.1KHz at 16-bit sample rates is just under 10MB per minute - a 650MB CD holds about 74 minutes of of Red Book audio and a 700MB CD holds about 80 minutes.

The other PC audio formats were created to reduce the filesize.  Back when storage and RAM was expensive, a 3 minute music track would take up about 30MB of drive space.  When 1GB hard drives were the norm, this was a *LOT* of space.  So, methods were used to reduce the filesize.  MP3 became the most popular format as the savings ratio was about 10:1 and the audio quality loss was not too bad.  MP3 and many other PC formats are known as "lossy" formats - the resulting MP3 is not a bit-for-bit representation of the original file.  During "compression", the MP3 encoder selectively removes parts of the audio track using somewhat complex algorithyms.  Unlike WAV files, you select bitrate in terms of kilobits per second rather than a sample rate.  The most common is 128kbps as this is the lowest you can go without starting to *really* notice the audio quality loss.  To "tin" ears, this means nothing.  But, to a trained ear and audio affectionists, MP3's @ 128kbps is like listening to a CD re-recorded on an old 78 Victrola.  AAC's compression saves much more of the original audio at the same bitrate as MP3, so an AAC compressed at 128kbps sounds as good as an MP3 recorded at 160kbps (some even say 192kbps).  Apple's iPod and iTunes uses AAC as their native formats.  AAC also includes complexity settings that allow you to fine-tune the AAC compression engine to the type of audio being sampled/compressed.  BTW, AAC is based on the Mpeg-4 audio algorithym and is a licensed product...that's one reason why more devices playback MP3 and WMA than AAC...license costs less.

But, if you're a serious audiophile who wants to preserve the original quality of a WAV file, then you need to look at a "lossless" format.  However, lossless formats don't compress as well as lossy formats, so you don't save as much drive space.  For example, Monkey's Audio (.APE) is a popular lossless format.  On average, an .APE file will be about 1/2 the size of the original WAV.  50% savings isn't bad, but a 30MB WAV still takes up 15MB drive space in .APE format (and 15MB could store five 3MB MP3's).  But, you'll be sure that the audio, once decompressed, is bit-for-bit identical to the original WAV file.  FLAC is another popular lossless format.

Anyways, getting back to burning an Audio-CD...

What you need to do is verify that the software you're using is set to burn an Audio-CD, aka CD-Audio, aka Red Book audio CD.  Some software will say that an "MP3 CD" is an audio CD...technically, this is true, but it's not a Red Book audio CD and will only playback on newer CD-Players that support MP3 files.  The key is in the amount of audio you can fit on a CD - 74 minutes for 650MB discs, 80 minutes for 700MB discs.  If you can fit more (without "tweaking" the software), then it's probably an MP3 CD you're creating.  Once you've burned the audio CD, Windows should show the audio files as .CDA files of 4KB each.  Audio CD's tracks don't have filenames, so Windows just creates a placemarker describing each track.  It was actually an early form of simple copy protection that prevented you from just copying the .WAV file and burning it to another CD - perfect copy each time with no generation loss.

Soooo, check your software settings and make sure you're burning audio CD's.  If you view the CD in Windows and see anything else than .CDA files, then they weren't created as audio CD's.



BTW, this would be the "workflow" I would use...

1. Setup and connect tape player to PC (many different ways to do this step!).

2. Using some audio mixing app (such as Audicity), capture the audio from the tape one track at a time.  Save each track as a .WAV file to prevent quality loss.

3. Using a CD-burning program (such as NERO), create an Audio-CD compilation and place the tracks I just captured into the compilation.  Pay attention to the available space used/remaining on the CD.

4. Save the compilation file.

5. Burn the compilation to a CD (or a .ISO file).

6. Test the burned CD on the PC.

7. Test the burned CD on a CD-Player.

One more thing...due to *MANY* variations of drives, CD-R media, and other things, not all burned CD's will playback on all CD-Players or CD-ROM drives, especially older ones.  Keep this in mind if a particular disc won't playback on a particular player/drive.


73,

  - Aaron, NN6O



-----Original Message-----
Sent: Sunday, February 17, 2008 6:25 AM
Subject: Re: [Ham-Computers] cd conversion

Thanks, you are being a BIG help.  I am Not at all familar with computer 
workings. SOoo What is an MP3?  Could they play in an external CD player?  I 
was once told " the only stupid question is one that you never asked" 
...Jerry