Brian Gaff wrote:
Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You tend
to get level overshoots and undershoots and an obvious worsening of the
noise performance on louder recordings
I never really understood why everyone went to Dolby,

I remember when Dolby B first started appearing on cheaper Japanese cassette
players. It solved the hiss problem by simply slicing off everything above 8k.
Of course these days that wouldn't bother me...unfortunately

On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

Brian Gaff wrote:
Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You tend
to get level overshoots and undershoots and an obvious worsening of the
noise performance on louder recordings
I never really understood why everyone went to Dolby,

I remember when Dolby B first started appearing on cheaper Japanese cassette
players. It solved the hiss problem by simply slicing off everything above 8k.
Of course these days that wouldn't bother me...unfortunately

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't. With a good deck, good tape, careful alignment and a low
recording level it was possible to get a flattish response to18-19k.

The problem was that the decks had to be carefully set up in
conjunction with the tape that was to be used, other wise the
processing exacerbated frequency response variations.

BTW Dolby B only operates at low recording levels; at high recording
levels the FR errors should only be those due to the inadequacy of the
machine/tape.

Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

Brian Gaff wrote:
Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You tend
to get level overshoots and undershoots and an obvious worsening of the
noise performance on louder recordings
I never really understood why everyone went to Dolby,
I remember when Dolby B first started appearing on cheaper Japanese cassette
players. It solved the hiss problem by simply slicing off everything above 8k.
Of course these days that wouldn't bother me...unfortunately

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.

But on these decks it did because with the Dolby off there was response up to at
least 12k whereas with it on it didn't just remove the hiss it removed
everything..as per my not properly implemented comment.


With a good deck, good tape, careful alignment and a low
recording level it was possible to get a flattish response to18-19k.

I think that's Nakamichi terroritory and a few other *very* high end decks only,
certainly not cheap.

The problem was that the decks had to be carefully set up in
conjunction with the tape that was to be used, other wise the
processing exacerbated frequency response variations.

Yes my point in saying 'cheap' was that it hadn't been properly implemented

"bcoombes" bcoombes@orangedotnet wrote in message
...
Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.

But on these decks it did because with the Dolby off there was response up
to at least 12k whereas with it on it didn't just remove the hiss it
removed everything..as per my not properly implemented comment.


What tolerance was there on the response up to12k?, and at what rate did the
response fall off above 8k with Dolby on? What level, relative to Dolby
level, did you make your measurements at?

Removing everthing above 8k wouldn't make much difference to the hiss
anyway, as audible hiss is mainly in the 2k- 10k region

David.

David Looser wrote:
"bcoombes" bcoombes@orangedotnet wrote in message
...
Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.
But on these decks it did because with the Dolby off there was response up
to at least 12k whereas with it on it didn't just remove the hiss it
removed everything..as per my not properly implemented comment.


What tolerance was there on the response up to12k?, and at what rate did the
response fall off above 8k with Dolby on? What level, relative to Dolby
level, did you make your measurements at?


Hardly necessary since what was missing was/is clearly audible. As it happens I
still have a Panasonic RQ-X20D cassette player which I've just dug out of
storage and had a listen to to confirm the effect and it's totally obvious, with
the Dolby on some of the 'music' is just plain MISSING. My original 8k figure
was a [mis]remembered estimate, it actuallity it must be lower than that.
ISTR that Panasonic were established to be one of the manufacturers that took a
while to get the *new* Dolby technology right but the defect was quite common
for a while and was often commented on in reviews of cassette decks of the time.

bcoombes wrote:
David Looser wrote:
"bcoombes" bcoombes@orangedotnet wrote in message
...
Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.
But on these decks it did because with the Dolby off there was
response up to at least 12k whereas with it on it didn't just remove
the hiss it removed everything..as per my not properly implemented
comment.


What tolerance was there on the response up to12k?, and at what rate
did the response fall off above 8k with Dolby on? What level, relative
to Dolby level, did you make your measurements at?


Hardly necessary since what was missing was/is clearly audible. As it
happens I still have a Panasonic RQ-X20D cassette player which I've just
dug out of storage and had a listen to to confirm the effect and it's
totally obvious, with the Dolby on some of the 'music' is just plain
MISSING. My original 8k figure was a [mis]remembered estimate, it
actuallity it must be lower than that.
ISTR that Panasonic were established to be one of the manufacturers that
took a while to get the *new* Dolby technology right but the defect was
quite common for a while and was often commented on in reviews of
cassette decks of the time.

On the above subject here's some technical stuff on Dolby NR implementation
problems. No doubt many of the early and 'cheap' cassette decks *incorporated*
them but it seems it may also be a problem with the recordings. Any comments
from some of the people here who obviously know about this stuff gratefully
received since I'm more interested in learning than 'being right'.

1. Pumping:
Incorrect selection of the control path bandwidth external components can result
in an audible increase in noise as the input level changes. This is most likely
to be heard on solo instruments or on speech. Sometimes the S/N rate is too poor
and masking will not be completely effective - i.e., when the bandwidth is wide
enough to pass the program material, the increase in noise is audible. Cutting
down on the pumping will also affect the program material to some extent and
judgement as to which is preferable is required. Sometimes a shorter decay time
constant in the detector circuit will help, especially for a source which always
shows these characteristics, but for better program material a return to the
recommended detector characteristics is imperative.
2. High Frequency Loss:
This can be caused by an improper control path gain setting—perhaps deliberate
because of the source S/N ratio as described above—or incorrect values for the
audio path filter capacitors. Capacitors larger than the recommended values will
scale the operating bandwidth lower, causing lower -3 dB corner frequencies for
a given control path signal. Return to the correct capacitor values and the
appropriate control path gain setting will always ensure that the h.f. content
of the signal source is preserved.

"bcoombes" bcoombes@orangedotnet wrote in message
o.uk...
bcoombes wrote:
David Looser wrote:
"bcoombes" bcoombes@orangedotnet wrote in message
...
Bill Taylor wrote:
On Sun, 10 Jan 2010 10:22:12 +0000, bcoombes bcoombes@orangedotnet
wrote:

The cassette deck might have sliced everything above 8k off, but Dolby
B didn't.
But on these decks it did because with the Dolby off there was response
up to at least 12k whereas with it on it didn't just remove the hiss it
removed everything..as per my not properly implemented comment.


What tolerance was there on the response up to12k?, and at what rate did
the response fall off above 8k with Dolby on? What level, relative to
Dolby level, did you make your measurements at?


Hardly necessary since what was missing was/is clearly audible. As it
happens I still have a Panasonic RQ-X20D cassette player which I've just
dug out of storage and had a listen to to confirm the effect and it's
totally obvious, with the Dolby on some of the 'music' is just plain
MISSING. My original 8k figure was a [mis]remembered estimate, it
actuallity it must be lower than that.
ISTR that Panasonic were established to be one of the manufacturers that
took a while to get the *new* Dolby technology right but the defect was
quite common for a while and was often commented on in reviews of
cassette decks of the time.

On the above subject here's some technical stuff on Dolby NR
implementation problems. No doubt many of the early and 'cheap' cassette
decks *incorporated* them but it seems it may also be a problem with the
recordings. Any comments from some of the people here who obviously know
about this stuff gratefully received since I'm more interested in learning
than 'being right'.

1. Pumping:
Incorrect selection of the control path bandwidth external components can
result in an audible increase in noise as the input level changes. This is
most likely to be heard on solo instruments or on speech. Sometimes the
S/N rate is too poor and masking will not be completely effective - i.e.,
when the bandwidth is wide enough to pass the program material, the
increase in noise is audible. Cutting down on the pumping will also affect
the program material to some extent and judgement as to which is
preferable is required. Sometimes a shorter decay time constant in the
detector circuit will help, especially for a source which always shows
these characteristics, but for better program material a return to the
recommended detector characteristics is imperative.
2. High Frequency Loss:
This can be caused by an improper control path gain setting-perhaps
deliberate because of the source S/N ratio as described above-or incorrect
values for the
audio path filter capacitors. Capacitors larger than the recommended
values will scale the operating bandwidth lower, causing lower -3 dB
corner frequencies for a given control path signal. Return to the correct
capacitor values and the appropriate control path gain setting will always
ensure that the h.f. content of the signal source is preserved.


In the mid 80s, I owned a HiFi shop, and sold a lot of Nakamichi machines.
As part of the sale, I offered to line up the machine to the users'
preferred tapes. Few users understood that tape formulations differ, even
between batches of the nominally same tape. Nakamichis were truly excellent
machines, and were capable of exceptional performance, but, they had to be
immaculately lined up. Cassette generally is at the limit of what is
possible, and Nakamichis were at the limit of the limit.

Nevertheless, a machine could be lined up to give a 30Hz-20kHz -2dB
response, with a 60dB S/N ratio, well under 0.1% W&F and less than 3%
distortion at 1kHz and 0dB where 0dB was 200mM/mm all simultaneously using
Dolby C on metal tape, and with Dolby tracking to within 1dB. The big
however, was that changing tapes to another metal tape, say TDK from Maxell,
or That's (my favourite) to TDK would destroy the performance. Frequency
response, Dolby tracking, distortion, noise, would all get significantly
worse. Then the tape manufacturers wouldn't help by constantly "upgrading"
their tapes which meant that the machine's record side had to be lined up
all over again. I used to encourage customers to buy a couple of boxes of
tapes with their machine, to give them a fighting chance of having a stock
of tapes the machine was aligned for.

I often used to hear that Dolby was awful, that people preferred to record
without Dolby and play back with, or the other way round, that B was much
better than C etc etc. C was a LOT better than B, but was correspondingly
more critical of line-up (Dolby C was effectively two Dolby B processors in
series..the first implementation of Dolby C was actually that, then a
dedicated B/C chip became available which unfortunately wasn't totally
compatible with the first implementation. All the horror stories of Dolby
essentially came down to lack of alignment...you can't expect the Public to
line up their machine every time they used it, but that's pretty much what
it took if you wanted A-B transparency, which is what a freshly lined-up
Nakamichi could do. Few other machines gave you access to record EQ, record
and bias current, replay EQ, separate record and playback heads, head
positioning, dual capstans that took away the cassette's pressure pads etc,
and so their line-up was always compromised, if it ever happened.

With my own Nakamichi, I would do a full line-up every time I wanted to do a
"proper" recording, i.e. one to keep, but it became a real fag, and wasn't
sad to give up tape for PC recording.

S.

"bcoombes" bcoombes@orangedotnet wrote

Hardly necessary since what was missing was/is clearly audible. As it
happens I still have a Panasonic RQ-X20D cassette player which I've just
dug out of storage and had a listen to to confirm the effect and it's
totally obvious, with the Dolby on some of the 'music' is just plain
MISSING. My original 8k figure was a [mis]remembered estimate, it
actuallity it must be lower than that.
ISTR that Panasonic were established to be one of the manufacturers that
took a while to get the *new* Dolby technology right but the defect was
quite common for a while and was often commented on in reviews of cassette
decks of the time.

What you were hearing was dynamic expansion of the HF. The HF isn't
"missing" exactly, but it has been pushed down in level by up to 10dB,
depending on it's frequency and on it's original level. The audible effect
is unpleasant IMO, probably subjectively worse than the simple HF roll-off
you took it to be.

I long ago gave up using Dolby NR on cassettes; I have a fairly up-market
Aiwa with auto bias and eq adjustment, but even with that I preferred to
sound with Dolby off. A little bit of tape hiss is pretty innocuous, far
less subjectively disturbing than hearing NR systems at work.

David.

David Looser wrote:
"bcoombes" bcoombes@orangedotnet wrote
Hardly necessary since what was missing was/is clearly audible. As it
happens I still have a Panasonic RQ-X20D cassette player which I've just
dug out of storage and had a listen to to confirm the effect and it's
totally obvious, with the Dolby on some of the 'music' is just plain
MISSING. My original 8k figure was a [mis]remembered estimate, it
actuallity it must be lower than that.
ISTR that Panasonic were established to be one of the manufacturers that
took a while to get the *new* Dolby technology right but the defect was
quite common for a while and was often commented on in reviews of cassette
decks of the time.

What you were hearing was dynamic expansion of the HF. The HF isn't
"missing" exactly, but it has been pushed down in level by up to 10dB,

Yeah that's right, it was only half as loud, maybe my choice of 'sliced' to
describe the effect was a bit OTT but it's the pushed down level wot I meant guv.

depending on it's frequency and on it's original level. The audible effect
is unpleasant IMO,

I quite agree, that's why I remembered it after all this time.

probably subjectively worse than the simple HF roll-off
you took it to be.

And I said something about HF roll-off where exactly?

I long ago gave up using Dolby NR on cassettes; I have a fairly up-market
Aiwa with auto bias and eq adjustment, but even with that I preferred to
sound with Dolby off. A little bit of tape hiss is pretty innocuous, far
less subjectively disturbing than hearing NR systems at work.


Currently I have a Denon 540 which sounds great to my (admittedly f***ed) hearing.

--
Bill Coombes

"bcoombes" bcoombes@orangedotnet wrote in message
...
Brian Gaff wrote:
Now, don't get all hot about it.
I have a dbx recorder or two here, and one can actually record bandwidth
limited squarewaves at higher levels. The one artefact you tend to see of
cours, is down to the finite time the processor takes to do things. You
tend to get level overshoots and undershoots and an obvious worsening of
the noise performance on louder recordings
I never really understood why everyone went to Dolby,

I remember when Dolby B first started appearing on cheaper Japanese
cassette players. It solved the hiss problem by simply slicing off
everything above 8k. Of course these days that wouldn't bother
me...unfortunately

Except that that's not what Dolby B does.

In playback Dolby B reduces the level of low-level HF by around 10dB. That
*should* be compensated for by an equivalent boost in HF during recording,
though if the alignment isn't good level mistracking will occur. If there
was no boost at all during recording then low-level HF, from about 3k (not
8k) upwards (but not high level HF) will be dropped in level by about 10dB.

David.