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FAQ:* Recording 7/07 (part 7 of 13)

( Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Part9 - Part10 - Part11 - Part12 - Part13 )
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Archive-name: AudioFAQ/part7
Last-modified: 2007/07/12
Version: 2.17

See reader questions & answers on this topic! - Help others by sharing your knowledge
14.0 Recording
	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 3 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).  Longplay mode cuts
	frequency response to 14kHz but adds even more recording time.

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 October 1996, DCC is quite affordable in price.  Some
	DCC home recorders are under $200.  However, blank DCC tapes
	are still hard to find and fairly expensive ($10 each for 90
	minute lengths).  Also, DCC manufacturers are dropping DCC
	from their lines, indicating that it is either on the way
	out or never made it in.

	Although the ability to play analog cassettes is a strong
	advantage of DCC, many people have had trouble with oxide
	particles falling off analog cassettes and clogging the gap
	of the DCC head.  This may be due to the extremely low
	quality of some analog cassette tapes and may be due to the
	very tiny gap of DCC heads.
	Caution: NEVER demagnetize DCC heads.  This will permanently
	damage the heads.

	As of May 1997, Philips has announced plans to discontinue DCC.

14.3 What about writable compact discs? What is the status today?
	Recordable and rewritable CD recorders and discs are available,
	and costs are dropping.  As of Dec 2003, recorders have shown
	up for <$30 and blank disks are advertised as low as $0.25
	each in bulk.  Many people report destroying many disks before
	getting their machine working correctly, but once people learn
	the software and hardware steps, archival CDs can be made
	inexpensively and routinely.  There is definitely a difference
	in discs and a difference in recorders.  However, it is tough
	to generalize on which are better or worse other than to say
	that name brand discs are a safer bet than off-brand discs.
	For more on CD-R read this excellent document:

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. 

	Dolby Corporation has developed other techniques and other
	acronyms for products related to surround sound.  The phrase
	"contains Dolby" isn't as meaningful today as it used to be.

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.
	It is very difficult to hear any degradation from PASC, but it 
	is possible, depending on the source and listener.  The effect
	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.
	DCC recorders do have digital inputs so can make one perfect
	copy of a master, but copy protection prevents digital
	duplication of a copy.

	For more information on audio compression, consult these 
	articles (courtesy of Jonas Palm):

	R. Veldhuis, M. Breeuwer, R. van der Waal, "Subband Coding of
	Digital Audio Signals  Without Loss of Quality,"  IEEE ICASSP,
	1989, pp. 2009-2012.

	J. Johnston, "Perceptual Transform Coding of Wideband Stereo 
	Signals," IEEE ICASSP, 1989, pp. 1993-1996.

	G. Davidson, L. Fielder, M. Antill, "High-Quality Audio Transform 
	Coding at 128 kbits/s," IEEE ICASSP, 1990, pp. 1117-1120.

	J. Princen, A. Bradley, "Analysis/Synthesis Filter Bank Design 
	Based on Time Domain Aliasing Cancellation," IEEE Trans ASSP, 
	Oct. 1986, v. 34 n. 5, pp. 2161-2164.

	P. Duhamel, Y. Mahieux, J. Petit, "A Fast Algorithm for the 
	Implementation of Filter Banks Based On 'Time Domain Aliasing 
	Cancellation,'" IEEE ICASSP, 1991, pp. 2209-2212.

	J. Johnson, "Transform Coding of Audio Signals Using Perceptual 
	Noise Criteria," Journ. Acoustical Society of America, Feb. 1988, 
	pp. 314-323.

	2nd Draft-Proposed Standard on Information Technology Coding of 
	Moving Pictures and Associated Audio, document ISO/IEC 
	JTC1/SC2/WG11 MPEG 90/001, Sept. 1990.

	G.Thiele, G. Stoll and M. Link "Low bit-rate coding of high-quality 
	audio signals. An introduction to the MASCAM system." EBU Review  
	No. 230

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 
	incorrect cleaning.

	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:
		Tape Warehouse
		Chamblee GA

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.

	Carver made a remote with timer which could be programmed to
	start recording at a specific time, if you have a recorder
	with remote control capability.

	For the true nerd, there's the programmable remote sold as a
	Scientific Calculator, such as 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  in  /pub/usenet-by-group/comp.sys.hp48

	You can also 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 work correctly.

	You can also use a computer's hard drive to record audio.
	Cybercorder 2000 shareware ($19.95 to register) schedules
	recordings on the computer sound card Line-In jack.

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 
	see it.

	Some VCRs have azimuth correctors or Dynamic Track Following
	which minimize these problems (Philips V2000 and some VHS).

	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. Progress in HiFi has
	modern VHS HiFi equipment on par with the best analog cassette
	recorders and close to that of the digital formats. VHS HiFi
	suffers generational loss and noise, but because of the high
	quality of the AFM (HiFi) track, these generational losses
	are minimal and not as severe as those of audio cassettes.

	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
	level control.

14.20 What is the difference between VHS HiFi and Beta HiFi?
	To record the video and HiFi sound signals onto the same tape
	area, VHS HiFi uses "depth multiplexing", while Beta HiFi uses
	"frequency multiplexing".  That is, the FM signal for Beta HiFi
	occupies a different frequency band than do the Beta format's
	luminance and chroma signals, and is simply mixed with those
	signals and laid down on the tape by the video heads.  In VHS
	the luminance and chroma signals were too close together in
	frequency for this to work.  VHS HiFi uses a separate pair of
	heads on the spinning head drum to record the HiFi carrier. 
	These heads' gaps are shaped so that the HiFi carrier is
	actually recorded at a different depth in the tape than the
	luminance and chroma signals.

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 
	your system.

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.

14.25 Why do I have hum when I connect cable to my VCR (or TV), which is 
		connected to my audio system?
	What you are experiencing is probably a "ground loop", caused
	by multiple connections from your equipment chassis ground to 

	building ground.  Since disconnecting the cable or building
	antenna from the VCR eliminates the hum, the cure is simple.
	The following info talks about "the cable" but works the same 
	with a coax from a master antenna system.

	Go to Radio Shack and buy one each of:

	15-1253, "300-ohm TV-VCR Matching Transformer"
		This looks like a little box with two screw terminals
		and a push-on male F (coax) connector.

	15-1140, "75-ohm coax/300-ohm twin lead indoor/outdoor matching
		This is a longish box or tube, with a female F
		connector on one end and a bit of twin-lead coming from
		the other.  The twin-lead ends in a pair of what are
		called "spade lugs" (shaped like U's).

	Note: each of these part numbers may have a "B" or other
	letter at the end. These indicate slightly different details 
	of functionally equivalent parts.  Don't worry about it.

	Connect the two spade lugs on the -1140 to the two screw
	terminals on the -1253.  Make sure they don't touch each other;
	this shouldn't be difficult to get right.  This gives you the
	"isolator", with a female coax connector on one end and a male
	coax connector on the other.

	Just insert the isolator "in line" in the incoming cable lead.
	ie treat it as you would a (very short) extension cord.  You
	can do this right at the back of the VCR (or whatever the cable
	is hooked to).

	Only one of the two units called out here (15-1140) actually
	provides isolation.  Two of the 15-1253 units back to back will
	NOT work.  Two of the 15-1140 units back to back will work fine
	but will be less convenient.

	If you can't find these specific parts, and want to know if the
	substitutes you've found will work, test them with an ohmmeter,
	measuring from either the pin or shield of the coax side to
	either wire of the twin-lead side.  If it's not an autoranging
	unit, set the meter to its highest resistance range.  You want
	to see no connection (ie: infinite resistance, an open circuit)
	between them.  As with the parts described above, only one of
	the coax/twinlead adapters needs to pass the test.

	This trick runs the signal through a PAIR of baluns.  This is
	more than is absolutely required to solve this problem, and may
	weaken the signal slightly.  This should not be a problem on
	most cable systems.  But, some audio stores are beginning to
	carry a unit made expressly for this purpose.  It contains a
	single 75 ohm to 75 ohm isolation transformer.  This should
	introduce less signal loss.  It will also be better shielded
	than the two baluns (see next paragraph). Under $10 would be an
	appropriate price.

	The back-to-back baluns may allow "ingress".  That is, if you
	are near to a TV transmitter, the short length of twinlead may
	pick up broadcast TV signals and mix them with the cable,
	causing interference.  If you can find a prepackaged 75 ohm
	isolation transformer as described in the preceding paragraph,
	it should be better in this regard.

	Mondial is selling a unit dubbed the "Magic-1"; this does the
	same job but with three capacitors instead of transformers.  It
	is said to cause less than 1 dB of signal loss.  On the other
	hand, it costs about $90.

	Yet another solution is to attack the problem at the line-level
	audio connection between the VCR and the rest of your stereo.
	Radio Shack's stereo ground isolators (270-054) are made for
	this purpose.  These go in the line-level AUDIO connections
	between the VCR (or TV) and the rest of your sound system.  If
	both the line in and line out jacks on the VCR are connected to
	the sound system, you'll need two of these isolators.  They are
	audio frequency transformers and may add some distortion and
	frequency response error.

14.26 Is Binaural better than stereo?  What is Binaural?
 	Judge for yourself.  There are samples of binaural recordings
 	available for free download at:
 	According to the Binaural FAQ (slightly edited to save space):
 	"Binaural...record(s) music and sounds with two tiny
 	omnidirectional mikes at the entrance to the ear canals on an
 	artificial head...This includes even the fleshy ridges of the
 	outer ears which modify the frequency balance of sounds
 	depending on the direction from which they originate...
 	"...A stereophonic system...uses loudspeakers but requires an
 	infinite number of channels for perfect reproduction...
 	(Binaural) requires only two channels for perfect reproduction
 	but involves the use of a pair of head receivers [drivers] held
 	tightly to the ears for each listener.  All listeners with such
 	a system can be given the illusion of sitting in the best seat
 	in the concert hall.  Harvey Fletcher in the SMPTE Journal Vol.
 	61, September 1953."
 	"The binaural experience is striking, and requires no special
 	equipment besides stereo headphones and binaural recordings.
	However, the 'perfect reproduction' mentioned by Fletcher is
	not necessarily achieved by all listeners due to variations
	in dummy heads, headphones and individual hearing. The
	astonishing realism is heard by nearly all, even with the most
	inexpensive headphones. But many have trouble localizing sounds
	directly in front or in back, and for some the sounds seem to
	occur inside their skull (just as with listening to stereo on
	headphones) rather than outside. Better matching of HRTFs (Head
	Related Transfer Functions) can correct some of these problems,
	and with recent advances in digital signal processing there may
	soon be a solution. It would involve a processor similar to the
	Dolby Headphone circuit - which provides a virtual 5.1 surround
	field on ordinary headphones, but allowing for the proper EQ
	and phasing to map the binaural sounds seamlessly in a
	360-degree sphere around each listener."

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; Texas Instruments     |  Internet:
50 Phillippe Cote St.               |  Voice   : (US) 603-222-8541
Manchester, NH  03101 USA 

Note: Texas Instruments has openings for Analog and Mixed
Signal Design Engineers in Manchester, New Hampshire.  If
interested, please send resume in confidence to address above.

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Last Update March 27 2014 @ 02:11 PM