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Audio Problems - Part 1
Greetings from Roger
Macie,
As many of you probably know, I have been writing "Maintenance Tips" for
Prosource’s "PROfiles" newsletter. These have included such topics as
"Avoiding Head Clogs", "The Ultimate Standard", and "The Next Step". All
of these have been geared to the broadcast professional who makes his or
her living off their Betacamcorders. Prosource is a national video
production equipment dealer based in Connecticut. Please review these
articles, especially those that refer to The Macie Uniform Standard. Its
conception was discussed in "The Call for Uniformity" and is written
about in two successive articles.
The "The Next Step"
discusses specialty set ups that are currently available for Sony and
Ikegami digital cameras. The "Macie Uniform Standard", also known as
"The Dateline Look", has been used and recommended by some of the top
network magazine shows. It has had an absolute success. When you look
good, we look good.
If you have not visited us lately, you may be surprised to find how
comprehensive our Freelance Listing Guide is. Over 40 countries and all
50 states are listed. We recently got feedback from a freelancer in
Oklahoma who got hired for a CBS morning show by the booking guy who
uses only broadcastvideo.com's "Freelance Listing Guide" because of the
great crews he gets. Check it out.
Now for maintenance
tips
The best way to deal with
audio problems is to be on the look out for them. There are literally
hundreds of things that can fail, from microphone, cables, batteries,
audio head clogs from bad tape, to PC board level component failures.
Audio should be monitored through the camcorder monitor system because
that is the end link in the audio path. EE is best used to judge the
audio quality. Usually cable and mike problems are caught because of the
higher quality monitor circuits. This EE audio is processed and passed
to the linear audio record heads, and/or to the AFM (CH3 &4) audio
tracks which are recorded along with the video signal.
On the BVW, HL-V Betacam
camcorders and the dockable BVV-5s, there is a separate audio playback
head and circuits, which are used to play the audio. Thus the audio
being recorded is what you hear in the EE mode, and the confidence
playback is what you hear while recording in the PB mode. That is why
when you listen to the audio, you hear an echo which is due to the time
delay it takes for the recorded audio to reach the playback heads. You
will also note the poor sound quality audio playback. In order to keep
these decks small, compromises had to be made somewhere.
You judge the quality in the EE mode and use the PB or confidence mode
just to see if the audio made it to tape. That’s why it is important to
record zero level tone while in EE mode, then either check the PB
(confidence mode) while recording, or just rewind tape and playback the
tape. By the way, in the "PB" mode it is actually in the EE mode until
you hit record at which time it switches to the confidence playback
heads.
The playback level on the meter should be within 2 DB of the EE or
record level. A drop of 3 db or more usually means that there is a
partial or complete head clog. This is a material build up on either the
record or playback heads. Because of the two heads used, either the
recording is OK and the playback is bad, or the recording is bad and the
playback is OK. In a pinch, you can playback a known good tape and see
if the playback is good. If it is bad, then the recording you made is
probably OK.
Of course if you have access to a playback deck or a VA-500 playback
checker, that will verify the audio recording is OK. The playback
checker takes the audio signal from the record head, not the playback
head. That's why the quality is so much better.
To clean the heads, it's a simple matter of removing the VTR door and
wet cleaning the heads. A lint free cloth, or chamois (shammy) tip swab
and 99 % isopropyl alcohol is usually the best way to clean the head
surface. Note that the recording surface of the head is at the extreme
ends, or top and bottom of heads surface. The audio record head stack
also records the time code signal. (Our Camcorder Survival Kit has
everything you need to maintain your camcorders. It also includes a
training video showing the proper way to clean the deck.) If cleaning
doesn't seem to work, try another tape. If the tape you're using has
edge damage, you could have poor head to tape contact and have what
looks like a head clog.
Don't bother with a cleaning tape. This tape was designed to clean
primarily the video head tips not the stationary audio heads. What often
works in a pinch is to take a tape and fast forward it to the end then
rewind it. This has helped me in the field when I didn’t' have any
cleaning materials with me. Running thousands of feet of tape across the
heads has a tendency to remove any head clog.
I will be picking up from this point on the next newsletter. Good luck
and happy shooting.
Take care,
Roger |
