AOH :: AUDIO-07.FAQ|
Audio Frequently Asked Questions, Part 7
There are more different recording systems available today than
ever before. Digital and analog are both available to the
consumer. With the advent of consumer digital recorders, used
pro analog recorders are becoming available for surprisingly low
prices. Now may be the time for you to buy a microphone and
recorder and make your first!
14.1 What is DAT? What is its status today?
DAT (Digital Audio Tape) is currently the standard professional
digital format for 2-track digital recording. DAT had a
short-lived consumer presence, but never "made it". As digital
recorders have no tolerance for clipping, using a DAT recorder
takes a slightly different knack. The results can be worth it,
however, as DAT format offers the same resolution and dynamic
range as CDs. DATs record for up to 2 hours on a tape, and can
run at three different sampling rates: 32 kHz, 44.1 kHz
(for CD), and 48 kHz (the DAT standard).
14.2 What is DCC? What is its status today?
DCC is Philips' attempt to modernize the regular cassette. DCC
decks can play analog cassettes, and can record new Digital
Compact Cassettes. They use stationary heads (DATs use rotary
heads as do VCR's), and although they are digital, they use
lossy compression to fit all the data on the cassette. Although
DCC sound quality is far better than the 1960 standard cassette,
the DCC does not have the sound quality present in DAT or CD.
DCC may be a good choice for consumers who want to assemble mix
tapes for cars or walkmans, but is not suitable for any
professional applications. As of December 1992, DCC is very
new, DCC equipment is very expensive, and the ultimate future of
DCC is not assured.
14.3 What about writable compact discs? What is the status today?
Recordable CD's are available, but are very expensive. Blank
discs sell for approximately $35 each, and the recorders start
at around $6,000. These units are mostly used by recording
studios and other audio professionals.
14.4 What are Dolby B, C, and S, HX Pro, and DBX? Are they compatible?
Dolby B, C, S, and DBX are techniques for increasing the
signal/noise ratio of recordings. All work in similar ways:
they compress the dynamic range of the sound during recording,
then expand it back upon playback. As much as we would like
it to be otherwise, you only get correct reproduction if you
use Dolby B to play back a Dolby B tape. Same for Dolby C,
Dolby S, and DBX. Dolby HX Pro is the exception.
Dolby B works mostly with higher frequencies; it increases
their levels during recording and decreases their levels, and
the levels of high-frequency noise such as tape hiss, during
Dolby B tapes can be played back without Dolby B processing,
but high frequencies are over-emphasized and the sound will
be excessively bright. This can be compensated for to some
extent by turning down the treble control. Audio novices
often remark that commercially recorded tapes recorded using
Dolby B sound dull when played back with Dolby B; this is
because they are accustomed to the boosted high frequencies
they hear when playing these tapes without Dolby.
Dolby C achieves greater noise reduction (about 8-10 db) than
Dolby B by working with a greater range of frequencies and
altering relative levels more; this means that playing Dolby C
tapes back with no Dolby processing or with Dolby B, leads to
very bad frequency response and a sound that most people find
unpleasent. Dolby C may also be more sensitive to variations
among decks in exact frequency response, alignment, etc. Some
people find that tapes recorded using Dolby C sound best only
when played back on the deck on which they were recorded.
Dolby S works with an even broader range of frequencies than
Dolby C, and achieves slightly greater noise reduction. Its
has three advantages over Dolby C: (1) many people find that
tapes recorded and played back using Dolby S sound closer to
the original than tapes done using Dolby C; (2) tapes recorded
using Dolby S don't sound awful if played back on Dolby B decks,
and (3) Dolby S seems to be less sensitive to variations among
DBX is similar to Dolby B, C, and S, but uses the same compression
on all frequencies, high and low. However, DBX is mostly used
in the professional market. Very little home DBX equipment is
available, and some of that home equipment is no better than
comparable Dolby B home systems. All DBX systems are compatible
with all other DBX systems, but incompatible with Dolby. A DBX
tape will sound terrible without DBX processing during playback.
All compression/expansion systems suffer two problems. One is due
to the fact that compressors can't compress a loud signal before
they have heard a bit of it, so that little bit of loud signal
will get through uncompressed. Likewise, quiet passages will not
be expanded until after they are detected. These delays give rise
to an audible problem often called "breathing".
The other problem inherent in all compression/expansion systems
is that if there are any frequency response errors in the tape
recorder, they will be made worse by the compression/expansion.
For example, if there is a 2dB dip in frequency response at 1kHz
in the tape recorder, this will be accentuated to a 4dB dip if
the compressor is using a 2:1 ratio. So compression/expansion
trades noise for frequency response error. For that reason and
the previously mentioned breathing, some people prefer to use
their recorder without any noise reduction at all. They prefer
a bit of noise to the other errors.
Dolby HX Pro is not noise reduction and does not use
compression or expansion. HX Pro is a technique developed by
Dolby Labs to increase tape headroom by decreasing the bias
when recording signals with a large high frequency component.
This allows better transient response, particularly on less
expensive tapes, and requires no processing when the tape is
played back. Dolby HX tapes can be played back on any system
with no decrease in quality.
14.5 What is the best cassette deck under $400?
14.6 What is PASC? Can I hear the effects?
PASC (Perceptual Audio Sub-band Coding) is a data-compression
algorithm. It increases the length of recording that can be
stored in a given number of data bits by eliminating sounds that
the developers' research claims can not be perceived by human
listeners. Its most important component is the omission of
quiet sounds that occur at the same time and near the frequency
of louder sounds. It provides up to a 4x increase in the length
of recordings a given digital medium can hold; this is essential
to allow full-length digital recordings on DCC (and on MD, which
uses a different compression technique). It is not necessary
to translate CD data to analog before compressing it using PASC,
nor the reverse.
You CAN hear PASC, but it is very difficult, since it is not
a distinctive noise (like a hiss) nor a consistent diminution
(like a notch in a speaker's response), but a broad,
uncorrelated dropout in a changing collection of sounds that
are masked by sounds that you can hear very easily.
Since it is lossy, repeated PASC recording will cause
progressive loss, and this signal damage may become easily
noticeable. This is a side effect that recording companies
hope will have the effect of discouraging piracy via DCC.
14.7 What is SCMS? Can I hear the effects?
SCMS (Serial Copy Management System) is a copy-protection system
intended to stop rampant piracy of commercial recordings to
digital tape. SCMS allows the home taper to copy from a CD to a
digital tape, but prevents anyone from digitally copying that
new digital tape.
You CANNOT hear SCMS.
14.8 How can I bypass SCMS?
There are professional devices used by engineers to manipulate
the digital bitstream, but they cost several hundred dollars and
are not cost effective for consumers. If you need to make
perfect digital copies of digital copies, buy a professional
digital recorder. Pro models do not have SCMS, are more durable
than consumer recorders, and may have better quality electronics
than consumer models.
14.9 What's this about a tax on DAT?
Every digital audio tape recorder and every blank digital tape
sold in the USA is priced to include a "premium" or "tax". This
tax is collected by the US Copyright Office and distributed to
the recording artists and record companies that own the
copyrights to commercial music. These fees are supposed to
repay them for lost royalties.
Many believe that this "tax" is illegal, because it represents
an assumption that the buyer will use the recorder and tape to
violate a copyright, and not to record their own works. A
founding principle of the USA legal system is that everyone is
assumed innocent until proven guilty.
If you believe that this law is unjust, write your elected
14.10 Is it legal to copy an LP, CD, or pre-recorded tape?
In the US today, it may be legal to copy LP's, CD's, etc. for
your own private use (such as to copy a CD to play on your
walkman). UK law specifically prohibits this, but it is almost
never enforced. It is definitely not legal in the US, UK, or
almost anywhere else, to copy these sources for commercial
purposes, or to give the copies to others.
It is as of yet unclear whether you own the rights to sell
or give away a copy of a recording if you made the copy on media
which was sold with an included digital audio tax.
14.11 How do I clean and demagnetize tape heads?
First, a caution: DAT recorder tape heads are VERY fragile.
Before cleaning the heads on a DAT recorder, get specific
recommendations from a very knowledgeable source that is
intimately familiar with DAT head cleaning. In the internet,
a good source is the DAT-Heads-Digest FAQ. For more information
on DAT-Heads-Digest, see section 20.2, below.
To clean tape heads, use pure isopropyl alcohol and lint-free
swabs. Wipe the metal parts of the transport with alcohol
(DON'T wipe the rollers!) and allow them to dry. Throw the swab
away after use. Be exceedingly careful when cleaning the heads
on a DAT. DAT heads are notoriously easy to misalign by
Practical tape head demagnetizers are available for under $10.
Try to find one with a plastic coated tip. If you can't find
one which is plastic coated. you can slip a drinking straw or
plastic tube over the tip for the same effect. This plastic
will prevent the demagnetizer from scratching the head.
Before plugging in the demagnetizer, remove all tapes from your
working area and unplug the recorder. Hold the demagnetizer
away from the recorder as you plug it in. Slowly bring the tip
of the demagnetizer up to the tape head and slide it back and
forth across each tape head for five one-second strokes. Then
pull it away from the head slowly and go on to the next. After
demagnetizing the heads, use the tip on each metal tape guide
with a similar five strokes. Last, slowly pull the demagnetizer
far away from the recorder and unplug it. Recording engineers
use a demagnetizer before each recording session.
14.12 How do I adjust a tape recorder for best results?
Adjusting a tape machine for best results usually requires
special equipment and test tapes. Unless you know what you're
doing, leave it for a pro. If you are serious about doing it,
buy the service manual for your particular tape recorder. It
will list a detailed procedure, as well as describe the correct
test tape and tools.
As for setting of record levels, it is best to experiment with
different levels on different tape brands. Different
formulation will reach saturation for different levels.
Generally speaking, the transients on a Chrome tape should peak
at about +6 dB above 0, though some formulations can take
significantly hotter signals.
14.13 Where can I get new pinch rollers or drive belts?
Projector-Recorder Belt Company
Whitewater WI USA
14.14 What is a good rubber (pinch) roller cleaner?
Teac RC-1 available from
J&R Music World
59-50 Queens-Midtown Expressway
Maspeth NY 11378-9896 USA
800-221-8180 or 718-417-3737
Tascam Rubber Cleaner RC-2 available from:
14.15 How can I program a recorder to tape a radio broadcast?
Radio Shack and Panasonic make a clock/radio/cassette that can
be set to record at a specific time. Radio Shack also sells 120
minute cassettes, which can be used for 60 minutes per side.
The recorders are not high quality, and the long tapes are
fragile, but it works.
You can buy "appliance timers" at hardware stores that will
start and stop an appliance at a specific time. Radio Shack
sells fancier versions of the same thing for more money. Gadget
freaks love "X-10" control systems. These can be configured to
do the same thing. All require a recorder that can be left in
RECORD mode. Such recorders are identified by a "TIMER" switch
on the front panel. Many cassette decks have a TIMER switch for
use with timers.
This can be set to start a recorder at a particular time. As
the recorder will be started from a remote control rather than
by the power line voltage, no timer switch is required. Radio
Shack has a very similar product available for $99.95, may be
less on sale.
Damark also sells a learning remote with a built in on/off
timer and sleep timer. It can learn 17 commands per device on a
total of 5 devices and should be great for taping a few shows.
They also sell a 8 device remote with timer. As Damark sells
close-outs, these items may not be available in the future.
7101 Winnetka Avenue North
PO Box 29900
Minneapolis MN 55429-0900 USA
800-729-9000 or 612-531-0066
There is a similar learning remote available from MCM
Electronics. They call it a Lonestar Learning Universal
Remote, item 80-450, $24.95 on sale.
MCM Electronics (Speakers, A/V Repair Parts, Etc) (+) (C)
650 Congress Park Dr
Centerville Ohio 45459-4072 USA
513-434-0031 or 800-543-4330
Another timer-remote is the Fox 800 (approx. US $80 retail).
The Fox 800 was spotted at Damark 800-729-9000 for $30 in
March of 1995.
There is also a Carver remote with timer.
For the true nerd, there's the programmable remote sold as a
Scientific Calculator, the HP-48. Audio remote control
software for this fine adding machine exists. For more
information, consult the HP-48 FAQ. The HP-48 FAQ contains
pointers to a few remote control programs. The FAQ is archived
at site rtfm.mit.edu in /pub/usenet-by-group/comp.sys.hp48
Use a VCR for audio-only recording. Hook the audio in to the
output of a radio, tuner, or receiver. You may also have to
connect some video signal to the VCR so that the sync circuits
14.16 Will CrO2 or Metal tapes damage a deck made for normal tape?
No. They will work fine. They are no more abrasive than common
tape and may actually be less abrasive than very cheap tapes.
Recorders which are designed for CrO2 or Metal tape have
different bias settings and equalization settings to take best
advantage of the greater headroom and to give flat response with
these different types of tape. However, they use similar if not
identical heads as less expensive tape recorders. Almost all
tapes are in some way lubricated, and these lubricants minimize
wear and squeaking.
14.17 Why do my old tapes squeak in my car cassette deck?
One problem that will cause this is "binder ooze". The binder
is the glue which holds the oxide particles to the backing.
With time, this binder can ooze forward and actually get past
the oxide particles, so that there is sticky stuff on the
surface of the tape. When this sticky stuff goes past the
heads, it can cause a slight stick, which will sound like a
squeak. You won't feel it with your fingers, but it is there.
If you have a prized tape with this problem, consider baking
the tape in a home oven at a very low temperature, like 150F.
This might cure the problem by drying out the binder.
14.18 Is VHS Hi-Fi sound perfect? Is Beta Hi-Fi sound perfect?
The HiFi recording format is subject to two different problems:
Head-switching noise and compression errors.
To get perfect reproduction, the FM subcarrier waveform being
played back by one audio head must perfectly match the waveform
from the other head at the point of head switching if a glitch
is to be avoided. If you record and then play the tape on the
same VCR under exactly the same conditions, you have a
reasonable chance of this working. But if the tape stretches
just a bit, or you play it on another VCR whose heads are not in
exactly the same position, or the tracking is off, the waveforms
will no longer match exactly, and you will get a glitch in the
recovered waveform every time the heads switch. This sounds
like a 60 Hz buzz in the audio, which is often audible through
headphones even if not through speakers.
The same glitch will occur in the video waveform too, but since
head switching always happens during vertical retrace, you won't
The wonderful signal to noise ratio of VHS HiFi is achieved
through the use of compression before recording and expansion
after playback. The actual signal to noise ratio of the tape
itself is about 35 dB and a 2.5:1 compressor is used to
"squeeze" things to fit. Like all companders, this produces
audible errors at certain places on certain signals, such as
noise "tails" immediately after the end of particularly loud
Worse, compressors often have problems simply getting levels
right. That is, if you record a series of tones, starting at
-90 dB and working up in 1 dB increments to 0 dB, and then play
them back, you will almost invariably have level errors. The
trend from soft to loud will be there but the steps won't be
accurate. Two or three of your tones might come out at
essentially the same level, then the next one takes a big jump
to catch up or even overshoot.
For music, the result will be that the relative levels of some
instruments, passages, etc. will not be accurate.
This doesn't matter as much for movies, which tend to have
steady volume level. Also, movie enjoyment is rarely hurt by
these level errors. VHS and Beta HiFi is fine for reproduction
of movie and tv soundtracks. They are also perfectly fine for
non-critical audio applications. But VHS and Beta HiFi are not
serious competitors to DAT, CD, open-reel analog tape, or even a
high quality cassette deck.
14.19 How do HiFi VCRs compare to cassette recorders? DAT recorders?
VHS HiFi and Beta HiFi are analog recording formats which use
modulation techniques to record a video signal and a stereo
audio signal on a videocassette. The audio capabilities
typically surpass that of the "linear" audio tracks found on all
video recorders, thus the "HiFi" designation. "HiFi" is
essential for getting good sound quality on your video
recordings and out of pre-recorded videos.
HiFi is also touted as an excellent audio recorder for
audio-only (no picture) applications. On paper, the
specifications are typically superior to analog cassette but
inferior to DAT. In reality, the quality of HiFi video
recorders is better than low quality cassette recorders but not
as good as high quality cassette recorders when they are used
with noise reduction systems. In no case can a HiFi video
recorder compare to DAT. It suffers from generational loss and
Many people use VHS HiFi for recording radio broadcasts, since
VCRs often have built-in timers and can record for up to 9
hours. If you use a HiFi video recorder to record from an
audio-only source, beware that some decks will not function
properly without a video signal for synchronization. If you are
interested in very good quality sound, use a deck with manual
14.20 What is the difference between VHS HiFi and Beta HiFi?
VHS HiFi uses "depth modulation"; Beta HiFi uses "frequency
14.21 Is there any good reason to buy a HiFi VCR for common TV shows?
If you do not own a stereo TV, the purchase of a HiFi VCR will
give you the capability to listen to stereo TV broadcasts to
14.22 What is the best cassette tape?
One simple answer to this question is that the best tape is the
tape which was used to align your tape recorder. A second
simple answer is that more expensive tapes are frequently
better in terms of quality of the backing, durability of the
oxide, accuracy of the shell and guides, and life.
Background: When you make a tape recorder, you build electronic
circuits which have specific, non-flat frequency response.
These circuits correct for the non-flat response of the tape
heads, the recording process, and the tape. These circuits can
be adjusted after the recorder is made, but adjustment is
tricky, and may or may not be successful with every tape made.
The designer of the tape recorder picked one tape as their
standard when they did the design, and built that recorder
to work well with that particular tape. It may work better
with a different tape, but it won't necessarily sound the
best with what one person calls the best sounding tape.
From a review of frequently given answers to this question,
it is obvious that almost every brand of tape has its advocates.
Many brands also have their detractors. Maxell and TDK tend to
have a strong following, but that is in part because they own a
large share of the US tape distribution market.
14.23 What is the best Reel-to-Reel tape?
See 14.22. Just as cassette tape recorders are set up
specifically for one type of tape, reel-to-reel tape recorders
are equalized and biased so that they are best with one specific
brand and model of tape. Just as more expensive cassette tapes
will last longer and have less noise than cheaper ones, you can
expect fewer dropouts, better quality control, and lower noise
from more expensive reel-to-reel tapes.
The major brands in reel-to-reel tape include Ampex, Scotch
(3M), AGFA/BASF, and Maxell.
14.24 What is Type I, Type II, Type III, and Type IV cassette tape?
These are IEC (International Electrotechnical Committee)
standards. They provide broad standards for all tapes,
and end the need to align a deck for an individual tape.
Type 1 is for normal "iron oxide" tapes (Fe2O3), Type 2
is for high-bias "chromium oxide" tapes (CrO2), Type 3
(obsolete) is for FeCr (ferric chrome), and Type 4 is
for Fe (Metal). Type 2 tapes tend to be more expensive
than type 1, and type 4 tapes are the most expensive.
This is because type 2 tapes tend to have less noise and
flatter high frequency response than type 1, and type 4
tapes tend to have even flatter highs and even less noise.
Some Type 1 tapes are more expensive than other Type 2 tapes,
and may be worth the extra price. More expensive tapes come
in better shells, have better lubrication, fewer dropouts,
smoother frequency response, and better uniformity from tape
to tape. Even though the types imply a particular tape
formulations, the type really refers to the tape performance.
For example, some iron oxide tapes have an unusual oxide
formulation with very small grains that conforms to the type
2 standard better than the type 1 standard. These tapes
will be labeled type 2, but may not have any chrome in them.
Most modern cassette recorders sense the tape type by the
holes in the back of the housing and adjust bias and
equalization to compensate for the differences. A few
top cassette recorders (the Revox and several Nakamichis)
automatically align to a particular tape by recording test
tones and then setting their own equalization.
In practice, each brand and model tape is slightly different.
For the very best recordings, adjust your recorder for the
tape you use most, or buy the tape which works best in your
recorder. Manufacturers adjust each recorder for a specific
tape at the factory. So the best tape might be the one
referenced in the recorder owner's manual. In a recording
studio, it is common to align the bias and equalization for
the specific tape used, and stick with that tape.
The information contained here is collectively copyrighted by the
authors. The right to reproduce this is hereby given, provided it is
copied intact, with the text of sections 1 through 8, inclusive.
However, the authors explicitly prohibit selling this document, any
of its parts, or any document which contains parts of this document.
Bob Neidorff; Unitrode Corporation | Internet: email@example.com
7 Continental Blvd. | Voice : (US) 603-429-8541
Merrimack, NH 03054-0399 USA | FAX : (US) 603-429-8564
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