I'm not so sure I want the error concealment of the DAT machine
making assumptions I can better control in Wavelab or
Samplitude--but, for many transfers the error CONCEALMENT is useful
and better than not using it. Archival purists might disagree. It's
all a matter of the content and its potential uses.
At 04:00 PM 2010-01-21, Tom Fine wrote:
>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.
>>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>.
>>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.
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.