[Ham-Computers] RE: Analong To Digital (long)

Wed, 28 Aug 2002 11:26:17 -0700

One often overlooked item when "defining" A to D, D to A, and D to D conversions is that the signal path is also involved.  At anywhere along the process, if the source is converted to analog, then the resulting copy, regardless if it's a digital medium, has gone through at least two conversion steps - the first from D to A, then from A to D.

So, in your situation, if you transferred the DAT contents to the CD-Burner via line-level (analog) connections, then "No", your copy wasn't digital to digital.  In fact, the CD-ROM you create will be a 2rd generation analog copy.  The original transfer from vinyl to DAT was the 1st gen copy, and the transfer from DAT to CD the 2nd gen.  Also consider that the resulting audio on the CD has gone through at least 3 conversions - A to D from vinyl to DAT, D to A from DAT to Burner, A to D from Burner to CD.  The quality of the AD and DA converters can be a significant factor in the resulting sound quality.  Most "audiophile" nuts look for Burr-Brown ADC's and DAC's in choosing equipment.  But, remember that audio is *very* subjective and each person's ear hears differently.

Now, if you're using digital connections between the DAT and CD-Writer, then theoretically, it should be a digital to digital transfer.  It then all depends on whether or not the devices themselves do any AD or DA conversions internally - they shouldn't; they usually just take the bitstream off the medium and send it directly to the digital outputs.

Duane, since you're no longer doing this via PC, you can skip this next section...it's here for reference.

When it comes to recording via a sound card, things get a little "messy".  The AD and DA converters on most soundcards are mediocre in quality.  For the average consumer (aka teenager with "tin" ears), this is fine.  However, for making good archival quality backups or transfers, a good ADC is required.  There are several "high end" digitizing only cards available out there for lots of $$$, but some more common sound cards also have fairly decent ADC's.  The original Ensoniq PCI adapter was a steal at $50 before Creative bought them and changed the rev on the ADC chip (I believe it was 1370 vs 1371).  Turtle Beach's current "Santa Cruz" PCI adapter uses a decent chipset from Crystal Semiconductor and has a good measured S/N ratio (around 90dB).  ESS and ADI SoundMax based sound cards generally have mediocre ADC's and lower S/N ratios and aren't good digitizing.  I'm not a fan of Creative, so I won't comment on their products as I might be biased <g>.  Yamaha based cards vary - some use Yamaha's internal ADC while others use an external ADC.

When actually recording a CD on a PC, you generally want to avoid the sound card's ADC.  The best way to do this is to use a digital input on the sound card, if available (most consumer sound cards don't have this).  By going through the digital input, the audio go directly to the target (HD or CD) as an uncompressed .WAV file which is basically the raw bitstream (this is the format CD's are written in).  If you use the sound card's analog inputs (aka Line or Aux in), then the written data would have gone through at least 1 conversion step - the A to D from Line-in to digital form saved on CD or HD.  And, since the sound card's ADC may be mediocre, the resulting .WAV file may also be mediocre.  Also remember that the line-level inputs are adjustable and it's quite easy to overload the ADC causing distortion and digital "trash" if set too high.  When using a digital to digital connection, there are no levels to adjust as everything is just a "one or zero" datastream.

When "ripping" audio from a CD, you generally want to take the .WAV file directly off the CD and not "capture" the audio from the CD.  Remember, the .WAV file on the CD is the raw bitstream and is the digital "master".  If you "capture" the audio via the sound card, then the CD-ROM drive will do a DA conversion from the CD and send it to the sound card as analog audio.  The sound card will then do an AD conversion and the resulting twice converted bitstream will be saved to the target (HD or CD).  Most CD-ROM drives on the market support "Ditial Audio Extraction", or DAE for short.  This allows the PC to grab or "rip" the .WAV file directly off the CD bypassing any DA or AD conversions.  However, most of these drives don't quite do this properly and the "ripped" bitstream has bit errors.  Single bit errors are normally not audible or are masked by the error correction scheme used by CD players, but if error exceeds the correctable length, you'll hear the error as distortion or digital trash (or worse, the CD-player will stop playing).  There are a couple of CD-ROM manufacturers that are well known for their DAE.  Plextor is the most well known - On their newest drives (paired with their ripping utility), they've gone as far as ensuring that any ripped datastream is a bit-for-bit exact replica of the original.  I've used Plextor drives for many years (back when they were known as "Texel") and the drives are solid, dependable, and still going (one of mine is now 10 years old!).  Customer Service is also excellent, but I digress... <g>.

There's a gentleman on the net that started a website a few years back.  He has tested many sound cards (and other ditigal products) much the same way the ARRL tests radios (by using actual test equipment).  You can get a general idea of how well your sound card will perform in digitizing audio if you visit his site.  He has the cards listed in order from best to worst.  He also has sound snippets from some sound card's MIDI wavetable set to give you an idea of what different wavetable samples sound like.  The site is at:

  http://www.pcavtech.com

It's worth a visit especially if you're shopping for a good sound card that's not just for gaming.

73,

  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {athsu}@unistudios.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"

-----Original Message-----
From: Duane Fischer, W8DBF [mailto:[email protected]]
Sent: Tuesday, August 27, 2002 5:41 PM
To: [email protected]
Subject: [Ham-Computers] Analong To Digital

I am learning much about the clever technical differences implemented by the
manufacturers of the CD burners used for audio reproduction. More on that later.

If I record a vinyl album to the Sony RCDW10, that is analog. However, if I
record the album to the DAT machine, is it not now a conversion from analog to
digital? Then if I copy the DAT tape to the burner is it not digital to digital?

Thanks.	

Duane Fischer, W8DBF	