Hi Richard:

I'm aware of the difference between correction and concealment. For usable audio, the concealment 
should be applied. My question was, is it applied in a direct-to-computer system and if not is there 
software to apply it so as to end up with an audio-usable copy? Granted, digital audio is "bits is 
bits," but if the end result is not usable audio, it's not very useful bits.

-- Tom Fine


----- Original Message ----- 
From: "Richard L. Hess" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, January 21, 2010 1:40 PM
Subject: Re: [ARSCLIST] DAT ripping


> At 06:41 AM 2010-01-21, Tom Fine wrote:
>>Ted, I understand the point of knowing about an error. But, does the tape-drive-to-computer method 
>>CORRECT the error for the purpose of USING the audio? That's the whole point of error-correction 
>>in the DAT machine design (and in CD players) -- to make the audio stream usable to the average 
>>listener. What is the point of transfer if the audio can't be used? So far no one has confirmed 
>>that the direct-to-computer method provides as good error correction abilities as just playing the 
>>DAT.
>
> Hi, Tom,
>
> Please do not confuse error CORRECTION and error CONCEALMENT. DAT, audio CD, CD-ROM, and DDS have 
> a layer of error CORRECTION. Audio DAT and audio CD have an error CONCEALMENT layer AFTER the 
> error CORRECTION to compensate for errors that were beyond the scope of the error CORRECTION. DDS 
> and CD-ROM, I believe, both have an extra layer of error CORRECTION. However, this is not 
> implemented on reading the audio media.
>
> In other words, both the DDS drive and the DAT player will have the same level of error CORRECTION 
> for the DAT (audio) tape. The DAT player will add error concealment which is not necessarily what 
> we want when making a preservation master.
>
>>As to Shai's point about multiple passes -- I too have had success once in a while re-playing what 
>>had been a dropout. It doesn't work all the time, but often enough that I'll do it with problem 
>>tapes.
>
> Yes, that can either get better or worse -- and cleaning can also help.
>
>>And yes, problem tapes can have the "error" indicator light flashing constantly or on for long 
>>periods of time yet recovered music stream flowing out.
>
> The "error" indicator comes on at some threshold within the capability of the error correction 
> protocol in most machines. The Panasonic SV3800s that I have provide a four-digit error readout. 
> Many machines have a two-digit error readout which is essentially the two left digits of the 
> four-digit readout on the Panasonic. I believe this is a hexadecimal readout, but I'm not sure at 
> the moment. However, on most playback of normal tapes, I get "error" readings up to let's say 02xx 
> and those are all correctable. Where I start to hear problems are around 07xx and higher. When I 
> made the tapes, I rarely saw errors as high as 0100. So any errors below that would not even show 
> on a two-digit machine. I think I remember being upset when I saw an error into the 004x region. 
> It stays for long stretches of time at 0000.
>
>>One other point -- you have the same mechanical issues with a computer drive as a DAT machine, no? 
>>It's the same method of a rotary head recovering data from a magnetic tape, isn't it?
>
> It's the same method of recovery, but the computer drive may (or may not) be more robust than the 
> audio drive/transport.
>
> If I recall properly, there were two different drum sizes that were somehow made to be compatible. 
> The porta-DATs had a drum of half the diameter of the studio/home machines. I'm keeping my D8 DAT 
> Walkman as an alternative for recovering some tape in the future where this might be a benefit.
>
> At 04:14 AM 2010-01-21, Shai Drori wrote:
>>Okay, that I understand, but I am thinking about correctable errors. We are then assuming that 
>>both systems will correct the errors the same way since both use the schemes implemented. How do 
>>we know which system has fewer errors over the other? My experience with rotary head systems is 
>>that sometimes second or third reading yielded better results, I think due to "cleaning" actions 
>>of the previous playing. Maybe we should compare five readings of the same cassette?
>
> As I understand it, the DDS tape readout software will flag any uncorrectable error in a log file 
> (which I've also referred to as a printout). I believe it logs it by A-time.
>
> I also recall that the DDS playback method will fail if there is no ATIME on the tape.
>
> As to your comment about correctable errors -- who cares where there were correctable errors as 
> they were corrected. All hard drives today have error correction and it's used regularly in normal 
> usage.
>
> Also, don't confuse analog playback with digital playback. With digital, all you need to do is 
> keep the error level within the correctable range and you're done. With analog, there is NO error 
> correction and you need to get everything absolutely as good as you can. The Drop Out COMPENSATORs 
> in analog (video) machines are the same as the error CONCEALMENT protocols in digital machines.
>
> In audio, our equivalent of "drop out compensators" was increasing tape surface area per unit 
> time. In pro video formats there was little option for changing track width or tape speed. In some 
> respects, that is why 15 in/s 1/2-inch 2-track with IEC equalization ended up being close to the 
> ideal stereo mastering format for analog audio. That seems to be the point where cost, 
> performance, low-frequency response, high-frequency response, noise, and azimuth wander are all 
> optimized. 0.2 inch x 15 in/s is 3 sq in/s of tape per track. Compare that to DAT or analog 
> cassette...you do the math <smile>.
>
> Cheers,
>
> Richard
>
> Richard L. Hess                   email: [log in to unmask]
> Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
> Detailed contact information: http://www.richardhess.com/tape/contact.htm
> Quality tape transfers -- even from hard-to-play tapes.