Treble loss in certain tape parts?
Teemu_K
into following problem: When I'm playing the tape it seems to fade out
all the treble. If I stop playing and put it back on again the lost
treble comes back. This problem seems to be afflicted only with
certain parts of the tape. Now, I'm not sure whether the problem is in
the someway ruined cassette or in the multitracker itself. Could this
be cause of magnetised playback head (I'm not sure what that is in
english) or ruined tape (it has been in heat and possible magnetic
field caused by mixers transformer). It is also possible that these
things don't cause the problem... Can the tape itself cause some
occasional "over magnetisation", which goes away when playback is
stopped and started again if it has somehow been ruined? I don't have
experience of demagnetising, is it harder or somehow different with
multitrackers and
how it is done?
I never have demagnetised heads but I think it's not the problem,
still a thing to do. Can someone help?
Big Craigie
Have you checked the actual physical state of the heads, guides and pinch
rollers. If they are dirty then that could affect the sound of the tape.
--
Big Craigie
Remove yourclothes to e-mail me
SMILIECHAMP
matters what kind of tape you use. if you a cheap tape then its not going to
give good sound with the highs,mid,and low and ya mic. so you should get a
better type of tape or something is wrong with 4-track
Teemu_K
> I have an old Yamaha MT44 multitrack recorder. Recently I have ran
> into following problem: When I'm playing the tape it seems to fade out
> all the treble. If I stop playing and put it back on again the lost
> treble comes back. This problem seems to be afflicted only with
> certain parts of the tape.
I forgot to mention that everything seems to be (and is) clean inside
the cassette compartment. Also I think the tape itself is not totally
poor because I got fairly good sound quality with it. It just started
to do this fade out thing and starting the playback again ensures that
the treble is not really lost from the recording.
Erwin Timmerman
This indicates that the tape tracking isn't right. Stopping and starting again puts the tape "in the right
place" so to speak, and then slowly it slips away again. Does it do this with all cassettes, or just with this
one?
It might be that the position of the head is off. However before adjusting it (there's a small screw next to the
head; be careful not to touch the head recording surface with your screwdriver though!!!) consider that it is
quite hard to get it back to the position that it is in now.
Re-adjust the head position gently while listening to a tape which contains lots of high stuff (acoustic guitar,
drums). The position is best at the spot with the most treble.
Good luck!
Erwin Timmerman
George Perfect
> I have an old Yamaha MT44 multitrack recorder. Recently I have ran
> into following problem: When I'm playing the tape it seems to fade out
> all the treble. If I stop playing and put it back on again the lost
> treble comes back.
This should tell you that the tape and the recording on the tape are OK
> This problem seems to be afflicted only with
> certain parts of the tape.
Which parts? Does it happen throughout the tape length or just near the
beginning or the end? Does it affect all tracks equally or are some
worse than others? Are all tapes affected the same or just one or two?
> Now, I'm not sure whether the problem is in
> the someway ruined cassette or in the multitracker itself. Could this
> be cause of magnetised playback head (I'm not sure what that is in
> english)
No - as the tape plays OK sometimes, it's not a magnetised head (your
English is fine, BTW).
> or ruined tape (it has been in heat and possible magnetic
> field caused by mixers transformer).
As the tape - presumably the sections concerned - plays back OK on
occasion, the tape itself is not the problem.
> It is also possible that these
> things don't cause the problem...
Now we're getting somewhere :)
The problem is caused by the tape moving a fraction of a millimetre away
from the playback head as it passes over it. If tape oxide (aka 'dirt')
is allowed to build up on the tape head this usually affects the whole
tape evenly - ie, you would hear a constant loss of treble.
As this problem comes and goes in your case - and affects different
sections of tape at different times - the cause is one of several
things.
First, an explanation :-
For any tape deck to work correctly, the tape must have intimate contact
with the heads. The changes in magnetic flux that occur as the tape
passes over the playback head extend for only a fraction of a millimeter
- hence, anything that moves the tape away from the head by even the
smallest amount will cause a fall-off in playback response. When this
happens on a large scale (ie, a piece of damaged tape moves more than a
millimetre or two from the head) you get a 'drop-out' or complete loss
of signal.
For reasons it's not necessary to understand now (just believe me!) as
the tape is moved away from the head, the fall-off in response is not
linear across the frequency spectrum but affects high frequencies first.
So, I hope you can understand that the root cause of your problem is
that the tape is losing contact with the playback head - ever so
slightly.
There are several things that can cause this:
1. Damaged tape. If the tape becomes damaged - eg; creased or its edge
becomes ragged - this will cause the tape to lift from the head as it
passes. You can visually inspect the section of tape affected to see if
it is damaged. But as, in your case, the same section plays OK when put
back in the machine, I suspect the tape is OK.
2. Poor quality tape. It's a little understood - and rarely considered -
fact that one of the primary qualities of any tape - especially a
cassette tape with its very fine tolerances - is that the tape WIDTH
must be even along the tape's length. Tape is manufactured in large and
very wide rolls. It is then cut down ('slit') to the width required as
it is wound on to the destination spool - the cassette hub in this case.
The machinery used to do the slitting must be of high quality and very
well maintained - in particular the knives that cut the tape must be
kept razor sharp - ie, replaced at regular intervals. As these are not
cheap, manufacturers of 'bargain' tape may run the knives longer than
optimum. Tape that is slit toward the end of the knives' life suffers
varying width as it is not cut cleanly. There are other mechanical
components and concerns in the slitting machines as well but this gives
you an idea. Tape is manufactured by several companies in the Far East.
If I tell you that the substrate and oxide coating used on premium
brands is identical to that used on cheaper brands because the tape is
in fact identical and has passed down the same production lines you
might get terribly excited at the thought of saving some money. But wait
- the cheaper tape was probably produced at the end of the batch. In
other words, the premium brand gets the tape that is produced just after
the productions machines have been cleaned and serviced - the cheaper
brand gets the blunt slitting knives, dirty rollers etc. that mean its
dimensional and magnetic tolerances will be far higher than the premium
brand. Now all those people here who regularly recommend only premium
brand tapes in multi-trackers have the knowledge to suport what they
have found by experience ;>)
3. Incorrect or erratic tape tension. HINT: this is the cause of your
problem. A little more explanation. In order to achieve and maintain the
very close contact between tape and head, the tape must have TENSION
applied within close tolerances. This is done by the capstan and pinch
roller pulling the tape evenly in a forward direction while at the same
time, the deck applies a small reverse force to the tape feed spool. On
high quality tape mechanisms, this 'reverse torque' is applied and
monitored electronically directly to the hub motor (assuming a three
motor transport). On cheap transports such as used in most cassette
multi-trackers and cheap cassette decks, the reverse torque is applied
via a mechanical clutch driven by a belt or rubber idler wheel. Any
reduction in the correct tension will alow the tape to 'bow' away from
the head - and cause the symptoms you are experiencing.
Right - having got to the (probable) cause of the problem, what causes
IT?
Let's deal with the serious (but, thankfully least likely) causes first.
Wear in the clutch or belt/idler mechanism can cause the tension to
increase and decrease seemingly randomly. If this is the cause of your
problem, you need to get the deck serviced - or, more likely, buy a new
one.
The casette itself is part of the transport mechanism - something that's
often overlooked. If this problem only occurs with certain tapes, then
you have to suspect either the cassette mechanism (the hubs and internal
tensioners play a large part in performance of the deck - another reason
to use only premium tapes) or variations in tape width. As in your case,
the same section of tape sometimes plays OK the cassette must be
suspected before the tape itself.
AND FINALLY FOLKS ... we come to the number one and most likely cause of
this problem - DIRT!!!
There's a very good reason why every tape deck manual tells you to clean
the heads and tape path REGULARLY.
ALL tapes shed some of their oxide coating throughout their lives.
Though worse when the tape is new, every time a tape passes through a
transport, some of its coating will be shed. This is fairly sticky stuff
and eagerly clings to the tape guides, roller and heads.
This stickyness applies to the outside as much as the bit that's
sticking to the roller or head. So ... it will try to stick to the tape
next time it passes.
The effect of this is that as the tape sticks to the dirt, the tension
(it is still being pulled by the capstan and pinch roller) increases
significantly. This can cause the tape to curve - usally the outer
tracks bow away from the heads. If this doesn't cause a problem, the
next bit will! As the tape "unsticks" it suddenly jerks forwards - very
effectively reducing the tension momentarily towards zero. This causes
the opposite effect and either the central tracks or all tracks are
affected as the tape straightens and moves away from the heads.
Dirt on tape guides and heads first shows itself as a dramatic increase
in wow and flutter along with 'micro-dropouts'. When bad, it can cause
the symptoms you complain of. Most people, IMHE put up with quite
staggering amounts of wow and flutter on cassette decks without
complaint. Only trained musicians with a very good ear (ie, not many
musicians!) recording sustained instruments such as piano or violin are
likely to complain. Your average axe wielding rock star can't hear many%
flutter and probably thinks 10% wow is due to the new stomp box he just
bought. Kool!
I digress.
Dirt also builds up on the capstan (the revolving metal pin on a
cassette deck that the rubber pinch wheel presses against). This shows
up as two bands of oxide where the edges of the tape pass by. As the
oxide is squeezed outside the tape contact area, some is transferred to
the rubber pinch roller. When both capstan and pich roller have even a
small pair of matching bands of oxide, the pressure the pinch roller can
exert on the tape (now running BETWEEN the bands of dirty oxide) is
greatly reduced.
The result is - once again - that the tape tension falls and the
symptoms you complain of start to appear.
What can you do?
I have explained several possible causes of your problem. If you have
the necessary test equipment and are of an academic mind, you could
perfrm some measurements of wow and flutter and tape tension to diagnose
the most likely cause.
I assume you have neither. Thankfully, there is a more pragmatic course
open.
You should THOROUGHLY clean the entire tape path including all tape
guides, rollers, heads and capstan. Use ONLY synthetic 'Q-tip' cotton
buds that have a very flexible stick and lint-free bud. The type that
has a strand of cotton wool wound round a stick are worse than doing
nothing - even a single strand of cotton fibre caught on a tape guide
will cause as much problem as several months of oxide build up.
For cleaning fluid, use pure isopropyl-alcohol. This is available from
most chemists/pharmacies very cheaply - or from most studio supply
companies more expensively. A small bottle will last years as you use
ONLY A TINY AMOUNT. If you prefer, you can buy proprietary tape head
cleaner - usually the same stuff with a little colour added and sold at
ten times the price.
DO NOT ALLOW ISOPROPYL-ALCOHOL OR ANY OTHER METAL TAPE PATH CLEANER TO
COME INTO CONTACT WITH THE RUBBER PINCH ROLLER OR OTHER RUBBER PARTS!!!
Dip the cotton bud into the cleaning fluid then let the excess fluid
drain off (you do not want fluid dripping inside the transport mechanism
where it might contact rubber belts or wheels or remove lubricant from
bearings). Then wipe the bud across the head or guide to remove the
dirt, ensuring that a clean face of the cotton bud is presented with
each swipe. Don't be tempted to re-use a dirty cotton bud - they cost
pennies so throw in the bin and use a fresh one.
The capstan can be cleaned with the deck turned on by holding a clean
cotton bud dipped in cleaning fluid against the capstan as it revolves.
DO NOT press PLAY as this brings the rubber pinch roller into contact
with the capstan. If your deck does not rotate the capstan unless a tape
is inserted, just clean the capstan while it is stationary.
Take great care not to use too much cleaning fluid as if any drips down
the capstan shaft it will quickly remove the lubricant from the capstan
bearing and you will soon be facing a hefty bill for repairs.
Metal rollers have to be held with your finger or other very soft tool
to prevent them rotating as they are cleaned. UNDER NO CIRCUMSTANCES
should anything hard or sharp (including wooden or plastic sticks) be
allowed to contact any part of the tape path.
The rubber pich roller and any other rubber parts are best cleaned with
a proprietary rubber cleaner. The term 'rubber' is used loosely here and
the components can actually be made of one of several different
compounds that unfortunately react differently to differing cleaning
fluids. Even proprietary rubber cleaner can be difficult to obtain these
days so in its absence, use simple soapy water. That means a solution of
ordinary (preferably non-perfumed) hand soap. NOT washing up liquid or
other detergents.
Again use a cotton bud dipped in the soap solution to clean the roller
while holding it still with a finger. When all the dirt is removed,
clean the soap residue off using a cotton bud dipped in fresh, clean
water. Continue until no more dirt or soap appears on the cotton buds.
Once you have cleaned the tape path as described - and allowed
everything to dry out for 20-30 minutes - it's time to try your cassette
again.
With luck, it will now play back normally.
If it still shows problems (and you are confident you cleaned EVERYTHING
in the tape path effectively) then suspicion must fall on the cassette
housing itself (check by recording and playing a known good quality tape
- a TDK SA or similar to listen for similar problems) or, sadly, the
transport clutch, belts or idler wheels requiring a trip to the service
centre.
If the cassette itself finally proves to be the culprit, the easiest
thing to do is to throw it away. But if it contains a valuable
recording, fear not - you can buy replacement cassette shells and with
care (get a service technician to do this if you aren't sure you can do
it yourself) you can remove the tape and hubs from the old shell and
transfer them to the new one. This should cure the problem and allow the
recorded material to be transferred to a more secure medium.
> Can the tape itself cause some
> occasional "over magnetisation", which goes away when playback is
> stopped and started again if it has somehow been ruined?
No. Don't lose any sleep over that thought!
> I don't have
> experience of demagnetising, is it harder or somehow different with
> multitrackers and
> how it is done?
Demagnetising (or 'degaussing' as it is often called) is always
performed the same way. You need a degaussing tool (a mains electricity
powered electromagnet whose core is extended to a tip that focuses the
varying magnetic field into a point). With the tape deck turned OFF and
disconnected from all audio connections, hold the degausser at least 2
metres (6 feet) away from the machine and turn it on (most have a button
or switch you operate with your thumb) then SLOWLY bring it toward the
machine and move it several times back and forth along the tape path -
making sure it comes close (be careful not to scratch heads and tape
guides if it doesn't have a protective coating on the tip) to all metal
parts - including tape guides, heads and rollers. Then JUST AS SLOWLY,
move the degausser away and turn it off ONLY when it is at least 2
metres (6 feet) from the machine. The degausser must be ON for the whole
time it is close to the machine.
> I never have demagnetised heads but I think it's not the problem,
> still a thing to do. Can someone help?
>
I hope I have.
--
George >{蚩髛<
Newcastle, England
(please remove leading 'x' from email address to reply, thanks)
Problems worthy of attack
Prove their worth, by hitting back - Piet Hein
George Perfect
Interesting thought ... but unlikely to be the cause of this particular
problem.
He should clean the machine first, then check the other issues I raised
in my long post in this thread.
Leave that screw well alone!
Adjusting azimuth by ear in this way is never a good idea for a lot of
reasons. If you want them, ask and I shall provide - but I think I've
provided enough verbage into the group for one day already! :)
George Perfect
> I forgot to mention that everything seems to be (and is) clean inside
> the cassette compartment. Also I think the tape itself is not totally
> poor because I got fairly good sound quality with it. It just started
> to do this fade out thing and starting the playback again ensures that
> the treble is not really lost from the recording.
>
In that case, look to the tape type (see comments about slitting process
in my lloooonnnggggg post) or the cassette shell.
Whatever the underlying cause, you have a tape tension problem.
If the machine truly is as clean as a whistle, it can only be the
cassette shell or - sadly - a failing tape transport requiring belt or
idler replacement or purchase of a new machine.
How old is the machine?
If you answer the other questions I and others have put to you we may be
able to help you more.
--
George >{ňżó}<
Teemu_K
> in my lloooonnnggggg post) or the cassette shell.
>
> Whatever the underlying cause, you have a tape tension problem.
>
> If the machine truly is as clean as a whistle, it can only be the
> cassette shell or - sadly - a failing tape transport requiring belt or
> idler replacement or purchase of a new machine.
>
> How old is the machine?
>
The machine is at least 20 years old and bought second hand. Inside is
maybe dirtier than I thought. (Now that I've read your long answer and
considering the fact that last time the machine was in service was in
1984). I have tested some other cassettes and so far have experienced
no problems. So far it seems that the problem was indeed a bad
cassette shell, though not sure yet. Their quality is going down with
increasing speed as the digital media is taking over.
Anyway, thank you for your long detailed answer, it really has helped
a lot. If cleaning and demagnetisation don't solve maybe re-occuring
problems then the problem is out of my hands and the MT44 heads to see
a qualified technician.
Erwin Timmerman
> Interesting thought ... but unlikely to be the cause of this particular
> problem.
>
> He should clean the machine first, then check the other issues I raised
> in my long post in this thread.
Indeed, that is a good idea. Interesting article BTW. I myself would only have come up with a question like this AFTER
a thorough cleaning job, so I kind of assumed that the tape path was clean. But then again, there are people who throw
mice away because they don't move smoothly anymore - or at all! - and never consider that the thing needs cleaning
inside (Knud, I mean computer mice, not live mice FYI). So suggesting it is indeed a good thing. Never thought about
the fact that this dirt buildup at capstan and pinch roller can cause loss of tape tension because they actually are
pushed apart by the dirt. But at that level the goo at the head itself is probably causing more hf loss than the loss
of tensioning does. Nevertheless a good thing to consider.
> Leave that screw well alone!
>
> Adjusting azimuth by ear in this way is never a good idea for a lot of
> reasons. If you want them, ask and I shall provide
Go right ahead :-) A few reasons I can think of:
1. The moment you touch it, you damage all recordings you ever have done on the deck because it is practically
impossible to get the head back into that exact position, thus playback of your previous recorded tapes will suffer.
2. You introduce a phase error between the left and right track that is hard to restore (see reason 1)
3. When you adjust the head a lot, the screw gets less tight and the head positioning will be even sloppier and will
eventually even change slightly during playback of one tape.
However, I sometimes get a tape from someone else I want to digitize. The azimuth is always a bit off on cassettes
recorded on other decks, so I sum to mono and adjust the head so that I get the best treble playback. When there are
no phase artefacts anymore, the head is pretty much in the optimum position for that tape. I have one dedicated deck
for this task because of reason 3, and indeed I have experienced the screw becoming looser al the time. But, so far so
good, I only use the deck for occasional transfers so it doesn't bother me to dig into it for tensioning the screw.
However, doing the same on a 4-track is almost impossible bacause all 4 tracks contain different material. Hard to
hear any phase problems when summing those to mono :-)
Erwin Timmerman
Carey Carlan
news:3EFBFB71...@stack.no:
> This indicates that the tape tracking isn't right. Stopping and
> starting again puts the tape "in the right place" so to speak, and
> then slowly it slips away again. Does it do this with all cassettes,
> or just with this one?
It is a tracking problem, but it probably has nothing to do with the head.
Clean the capstan and pinch roller.
What happens is that the tape is not being held straight as it pulls by the
capstan. It gets pulled slightly to one side which misaligns it with the
head and you lose high end.
If you try to set azimuth on the head, you will try to align it with this
skewed position which (a) probably isn't within reach of the adjustment
range of the screw and (b) will constantly shift, making exact tracking
impossible. In either case, you have messed up your head alignment to no
good end.
George Perfect
>
> > Interesting thought ... but unlikely to be the cause of this particular
> > problem.
> >
> > He should clean the machine first, then check the other issues I raised
> > in my long post in this thread.
>
> Indeed, that is a good idea. Interesting article BTW. I myself would only have come up with a question like this AFTER
> a thorough cleaning job, so I kind of assumed that the tape path was clean. But then again, there are people who throw
> mice away because they don't move smoothly anymore - or at all! - and never consider that the thing needs cleaning
> inside (Knud, I mean computer mice, not live mice FYI). So suggesting it is indeed a good thing. Never thought about
> the fact that this dirt buildup at capstan and pinch roller can cause loss of tape tension because they actually are
> pushed apart by the dirt. But at that level the goo at the head itself is probably causing more hf loss than the loss
> of tensioning does. Nevertheless a good thing to consider.
IME many people clean the heads but forget or ignore the tape guides and
rollers. On a good ol' big r2r deck you can easily see the result. When
I worked for Tascam back in the 70s I saw no end of tape decks coming
into the workshop whose heads were (almost) clean enough but whose
guides and rollers were caked with oxide deposits. In a really bad case
on a large deck you can see the tape stretching then snapping loose as
the capstan pull overcomes the friction - the feed spool can be seen to
jerk forward while the tape tension arms bounce off their stops.
Scale this down to cassette size and the same thing happens. It doesn't
have to get anywhere near close to being visually apparent for the tape
to move far enough off the heads to cause dropouts.
Ignoring cruddy cassette shells (that can be found even on premium
brands from time to time) probably the biggest overlooked area is the
capstan/pinch roller. It takes only a little oxide build up here to
drastically affect flutter and dropout performance.
> > Leave that screw well alone!
> >
> > Adjusting azimuth by ear in this way is never a good idea for a lot of
> > reasons. If you want them, ask and I shall provide
>
> Go right ahead :-) A few reasons I can think of:
>
> 1. The moment you touch it, you damage all recordings you ever have
> done on the deck because it is practically
> impossible to get the head back into that exact position, thus playback
> of your previous recorded tapes will suffer.
It's not "impossible" but the correct procedure to align a head for
azimuth is with a full-width recorded test tape and a dual-trace 'scope
in X/Y mode (or, these days I use a PC with a phase display). Done
correctly, this returns the machine to correct alignment.
In professional use an analogue deck would be regularly realigned with
such test tapes - as I still do with my Tascam and Studer machines.
> 2. You introduce a phase error between the left and right track
> that is hard to restore (see reason 1)
That's what incorrect azimuth alignment does.
> 3. When you adjust the head a lot, the screw gets less tight and the head positioning will be even sloppier and will
> eventually even change slightly during playback of one tape.
That shouldn't be a concern - unless you are very heavy handed, of
course ;)
>
> However, I sometimes get a tape from someone else I want to digitize.
> The azimuth is always a bit off on cassettes
> recorded on other decks,
There's a reason for that. Most cheap cassette decks have poorly
designed head mounting plates. I've certainly only seen one or two
designs in my time that get close to offering independent adjustment in
all three axes - or even two. IOW as one adjustment is made, the other
two are out of line. For this reason, many decks have no alignment at
all or offer only single axis alignment - relying on production
tolerances to set tilt, height and rotation.
If your deck has only a single adjustment screw, it's one of this type
and you should be aware that *wherever* you set the screw, it's unlikely
to be right as there is one and only one position where the head will be
in optimum alignment.
Ever tried repeating your test after running a tape through following
your initial alignment? If not, you may find it educational! And you may
decide to either (a) buy a better deck for transcription or (b) save
your time in future ;-)
> so I sum to mono and adjust the head so that
> I get the best treble playback. When there are
> no phase artefacts anymore, the head is pretty much in the optimum
> position for that tape.
Under those circumstances, that's as good a procedure as any, I suppose.
And this is why tapes recorded in studios are normally striped with tone
at the start of each reel - allowing levels and head alignment to be
checked and adjusted on a subsequent playback deck.
If you are doing this regularly, it's worth investing in a test tape and
a phase plugin for your computer DAW to realign the deck to optimum
between these sessions.
> I have one dedicated deck
> for this task because of reason 3, and indeed I have experienced the
> screw becoming looser al the time. But, so far so
> good, I only use the deck for occasional transfers so it doesn't bother
> me to dig into it for tensioning the screw.
If you do have a screw loose (!) fit a shake-proof washer. There would
normally be a spring washer or shakeproof washer on a deck designed for
regular adjustment. Cheaper decks have their screws sealed with Loctite
at manufacture and may not have the washer.
If your cassette deck's record/replay head is the type that has a fork
(or pair of fingers) type tape guide protruding from the left of the
head (when viewed from the front) you should be aware that there is
actually very little scope to adjust azimuth without causing bigger
problems as the guide presses the tape out of its natural path - you are
in effect adjusting head height (and therefore track alignment) as much
as azimuth.
>
> However, doing the same on a 4-track is almost impossible bacause all
> 4 tracks contain different material. Hard to
> hear any phase problems when summing those to mono :-)
That's why test tapes are recorded full-width. It then doesn't matter
which tracks you use to compare (though I usually use tracks 2 and 7 on
an 8-track deck) as the signals arise from the same recording.