DAT-Heads Digest #818, Volume #2 Fri, 21 Jun 96 19:12:02 EDT
From: "Alexander W. Chin" <firstname.lastname@example.org
Subject: Re: D7 need help on alignment, Beyond 20Khz and Analog Tape
Date: Sat, 22 Jun 1996 02:26:48 +1000
If you have access to a CRO (Oscilloscope) then it is simple. Take a tape
that you trust (possibly one you recorded when the D7 was new) and play it.
Hook input 1 of the CRO to TPRF and input 2 to TPSWP. Sync the CRO to input
2 and then just adjust the guides till you get the best looking envelope.
Simple. If you have no access to a CRO, you can put the deck in FF mode and
adjuse the right guide till you get good A-Time increments. If the guide is
too low, you lose A-Time in FF mode. Just raise it till you get A-Time
properly, and drop down to normal play and adjust the left guide till it
sounds right. Of course, it pays to take a piece of paper and draw down the
You are also assuming it is an alignment problem. It could be head wear. To
test this, take the D7 apart and perform this simple test:
i) Take pin 100 of IC 506 and ground it.
Then disconnet the ground and
ii) Take pin 100 of IC 506 and connect to pin 55/54 of IC 506.
While playing a tape, you should hear identical sound in both i) and ii).
If the D7 goes dead silent on either i) or ii), or the distortion is
markedly worse in i) or ii), then it is head damage (or wear). If the
distortion is equally bad then it is an alignment problem. Of course, it
would help a lot if you had a CRO, in which case you just compare A/B
Usual disclaimers apply - if you kill the D7, not my fault.
>From: Man on the Edge <email@example.com
>Subject: Re: Beyond 20Khz and Analog Tape
>Date: Thu, 20 Jun 1996 18:18:47 -0700 (PDT)
>> From: Mark Plancke <firstname.lastname@example.org
>> Subject: Beyond 20Khz and Analog Tape
>> Date: Tue, 18 Jun 1996 16:33:12 -0400 (EDT)
>> There is an interesting story that I came across in a Mix magazine article
>> in which they interviewed Rupert
>Before we all go off thinking that humans can hear sounds at 54kHz, we
>should perhaps consider other possibilities.
>1. If any part of this interference was digitized or if any part of
>the audio signal was digitized, you would DEFINITELY hear it! Unless
>you sample faster than 108kHz, this 54kHz noise would show up as low
Possible, but very very very unlikely. Most AD converters are oversampling
ones nowadays. The filtering is done by a digital FIR filter. The sample
rate is easily 64 fs or in some cases, 256 fs. This Nyquist frequency is
way above 54 kHz, (sample rate is about 3 MHz - 11 MHz). As for the digital
filter, 12 order eliptical is not uncommon.
Even if the filtering is done by analogue style filters, we are easily
talking 8-10 order filters and 54 kHz is more than an octave above 22.05
kHz, so the attenuation of the aliasing is in the order of -48 to -60 dB.
And then again, the aliased frequency of 54 kHz is around 10 kHz. Very hard
to hear I have to say.
>2. If this signal went through any transistor, diode, or any other
>exponential device (or even square law device), it could have easily
>been modulated down to audible frequencies. This is the most likely
>cause of the audible noise.
This I also don't think so. Any form of nonlinear modulation will result in
harmonics of higher order, not lower. Of course, I could be mistaken ...
now where did my textbook go? (I studied this in 3 rd year - about a year
>I simply don't think it's reasonable to assume that the 54kHz noise on
>its own added some mysterious unquantifiable "air" to the sound that
>cannot be otherwise established in laboratory tests on human hearing.
It is reasonable. In the early days of digital audio I could easily pick
out the difference between analogue and digital sound. 10 seconds of
listening to any source blindfolded, and I could tell you if it had been
digitised. I have a LP player (record player - vinyl). I still love the
sound of vinyl - it is very very different and has a certain characteristic
that digital doesn't have. I have tried DATing the vinyl and it sounds
I haven't pulled out a broadband spectrum analyser so I cannot tell you how
far the frequency spectrum of vinyl is (I would reckon around 30-40 kHz,
but I can't be sure). But it does sound different, and very different after
passing through a DAT.
This is not to say that digital sound is bad. It is maturing now, and for
consumer grade products, getting very very pretty darn good I have to say.
Probably in 5 years time, it would be indistinguishible from analog sound.
It is still different, but the differences are getting very small.
5 years ago, I could tell them apart in 10 seconds. Now it takes me about
3-5 minutes and I get the answer wrong about 25% of the time. That is how
good digital is getting.
Just my opinion.