Conference hips::uk_audioo

    
    I don't know about the real specs, but there's some information in this
    month's HFN/RR (where they review the Arcam Delta 150 NICAM tuner).
    
    From this article, it appears that the NICAM system works like this:
    
    - sample audio signal to 14 bit resolution (can't remember sampling
    frequency, might be 38Khz)
    
    - batch up sets of 32 14 bit samples.
    
    - based on the highest-amplitude sample in the batch, decide on a
    "scale factor", and scale each sample down to 10 bits by this factor.
    The scale factor is tacked on the front of the block, and is used by
    the receiver to reconstruct the 14 bit data at the correct amplitude
    level. This technique allows high resolution for low amplitude signals,
    and lower resolution for high amplitude signals.
    
    The article then briefly explains how this digital signal gets put onto
    the video carrier, but I don't really know enough about signal
    processing to understand how that works. The upshot of all this is that
    the audio signal has somewhat less resolution than CD.
    
    The article made some interesting points. The author made some
    cassettes from TV programs to listen to in his car. He said they
    sounded very strange when played without any visual cues as to what was
    actually going on. He complained in particular about spot mics being
    used and causing voices to appear in funny places in the resultant
    sound mix (although it sounds natural when you can see what's happening
    on the screen).
    
    Trevor

    How much is the Acrcam Delta 150 Nicam tuner?
    
    I have a Stereo video, but it's not Hi-fi quality.  i could use
    the auxiliary input to record TV in stereo.  The replay sound quality
    would be very inferior to that broadcast (although still in stereo).
    
    My cassette deck would be up-to the job, but I guess it would get
    tiring syncronising the audio to the visual recording when playing
    back!  (plus I would have to swap tapes at 45/60 mins max).
    
    Hmm?   
    
    Also, why do people buy NICAM televisions?  Must sound great live, but 
    surely the digital signal is lost when a program is recorded on a 
    normal (non-NICAM) video, and the television reverts back to normal
    sound?
    
    And another thing...  Why have both a NICAM tv and NICAM video?  Surely
    only a stereo TV would be required to monitor the stereo output (in the
    absence of a real Hi-Fi with auxiliary inputs).
    
    What do you think?
    Rob.

> 
>     How much is the Acrcam Delta 150 Nicam tuner?
>
    	350 pounds
    
>     
>     Also, why do people buy NICAM televisions?  Must sound great live, but 
>     surely the digital signal is lost when a program is recorded on a 
>     normal (non-NICAM) video, and the television reverts back to normal
>     sound?
    
    Yes.  Perhaps people aren't too worried about not getting NICAM on
    videos. 
    
    >      
    >     And another thing...  Why have both a NICAM tv and NICAM video?  Surely 
    >     only a stereo TV would be required to monitor the stereo output (in the 
    >     absence of a real Hi-Fi with auxiliary inputs).
    
    I agree - I think the best approach would be to have a NICAM VCR with a
    good tuner in it so that you can both record and watch NICAM if you
    want. You lose the ability to record one NICAM program and watch
    another as the same time in stereo, but who cares about that ?
    
    Of course, if you have a crappy old telly, and have recently bought a
    non-NICAM VCR (like me), you may favour replacing the TV first.
    
    Trevor

Ah, it's not just an audio tuner, but a video tuner as well.

ARCAM say that the audio/video circuit is of sufficiently high quality, that
it will improve the video signal by removing the audio signal from it.

Therefore, you should get a better picture. If you already have a video/TV,
then this extra tuner is cheaper than getting a NICAM video/TV, given the
low resale cost of older videos.

That doesn't mean to say I'm buying one!

    I recently (last 6 months) have bought a NICAM TV and a HIFI NICAM
    VCR. The TV came first and I was very pleased with the sound
    capabilities so when it came time to replace the Video I decided to
    opt for the Panasonic VF-B65 (there is mention of this in another
    note). In the previous note it was said that "TVs and VCRs don't seem
    to be designed with decent sound in mind" but I'm sure anyone else who
    owns either this or the B70 video will disagree as the sound quality
    when played through a Hi-Fi is superb.  
    
    I am very impressed with my set-up , on reflection I would probably not 
    have bought the NICAM TV if I had knew I was going to buy the VCR but 
    what's done is done and I certainly won't need to upgrade either in the 
    near future.
    
    
    							Geo.

I've had a Hi-fi video for a few years now and am very pleased with it, the
sound quality is sooper and makes me feel like I'm in the cinema even if I
do need a magnifying glass to see the TV screen.

However, the big problem with this format is tape dropouts and general
degradation which causes *extremely* irritating buzzing and 'fluttering'
noises. This is particularly noticeable when hiring virtually anything
other than recently released videos. Many's the time I've had to switch
back to linear mono sound because of this interference.

Do NICAM VCRs suffer in this respect? Also how do NICAM VCRs actually
record the sound? Do they record sound in encoded or decoded form
or both? If decoded, is it in the hi-fi format in which case I guess they
will be just as susceptible to the interference.

Steve.

I think .-1 has it slightly wrong.

NICAM is a way of getting the stereo information from the TV Aerial. Any
HiFi Stereo video recorder can record from it. This is why Arcam can supply
a NICAM decoder.

I know what you mean about the interference with sound. It does seem that
the tape has to be 'exactly right' for it to sound good. I've had a few tapes
where I've had to move to mono sound. Even tweaking the HiFi tracking control
didn't do much.

Mark.

In other words, a NICAM VCR is merely a Hi-Fi stereo video with a NICAM
decoder built-in?

So when I said that a NICAM VCR would be just as susceptible to the noise,
I was in fact, slightly right.

Steve.
;^)

re .15:

>    But surely (based on a previous reply), a non-nicam VCR can record the 
>    incoming signal (digtally encoded bit and all).  Then use the external 
>    decoder (a la Arcam) to extract the NACAM encoded signal, passing sound
>    to expensive Hi-Fi (you must have one of those since you're reading
>    this!) and picture minus sound to the TV/monitor.

No, I don't think this'll work.  I seem to remember the NICAM-encoded audio is
present in the RF signal, so you can extract it at the tuner's FM decoder
stage, but once you've decoded the FM to get a mono audio signal you've lost
the information required for NICAM decoding.  It's rather like making a mono
recording of an FM stereo broadcast; you can't get the stereo signal back
because you didn't record either the RF signal or audio L-R signal, only the
audio L+R signal.

    
>    Is the sound present in the VHF TV output from the Arcam decoder? (i.e.
>    does it remove it?)

I don't know if the Arcam has an RF output; if it does it'd certainly include
audio.  But audio will certainly not be present in the video output - there's
nowhere for it to go.  If it does have an RF output, I wonder if it passes the
NICAM information through?  I guess it has to, in case it's passed to a NICAM
TV.

    
>    If so, perhaps the picture is improved if you use the decoder to remove the
>    analogue soundtrack before the video.  Thus eliminating interferance of
>    sound on picture.

Arcam make much of the fact that audio and video are separated as early as
possible.  This means audio- and video-specific optimisation can be applied,
giving higher video, as well as audio, quality compared to typical TV or VCR
practice.  So if you use your TV as a monitor you may well get better a picture
than if you used its own tuner.

>    The other expensive alternative to improve picture quality is to have a
>    monitor and to use the <mumble> video output leads from the VCR (thus
>    eliminating two tuner circuits during tape playback).

I was kind of assuming this.  Modern TVs usually have video inputs, so they can
be used as monitors.  Certainly running through multiple tuners is a no-no. 
Personally, I'd like to use a professional broadcast monitor - you don't get
high light levels, or a flat screen, but the colour shading accuracy would be
wonderful.  I dread to think what one would cost, though.

Nick

    RE: .-1
    
    Hi Nick,
    I thought that the NICAM signal was actually transmitted as part of the
    picture image, mono 'normal' sound being separate.  So, a normal video
    wouldn't do anything with the NICAM signal except record it, as it does
    the rest of the picture.

I thought it had its own subcarrier, separate from both the mono audio and
video channel.  But anyway, if it's buried in the video signal, VHS doesn't
have enough bandwidth to waste on information that isn't visible.  It'll
certainly make a dog's breakfast of it, if its treatment of the picture is
anything to go by.  

Nick

The NICAM digital signal is encoded using DPFSK modulation onto a sub carrier
that is around 6.23 Mhz (if memory serves - the MAPLIN magazine ran a detailed
article about a year ago that has all the real figures and equations - I can
look it up if you like).

This Sub-carrier is therefore just above the 6.0 Mhz FM sound subcarrier that 
is used for the mono sound.

NON-NICAM VCR's (and TV's) have narrow filters that separate out the video and 
sound sub-carriers (prior to recording in case of the VCR) - hence they loose
 the NICAM subcarrier. 

I believe that true NICAM recorders (not the cheap one, which records the decoded signal using
 normal analogue - the small print points out that the recorded sound is stereo
 but NOT hi-fi) have different filters and can record the encoded NICAM 
 subcarrier signal - ie the recording is effectively digital.

THUS, if you play a true NICAM VCR recording/recorder into a NICAM TV, the TV's
NICAM light comes on and it's decoder decodes the sound - as well as being 
available from the Audio sockets on the VCR.

The reason for having both a NICAM TV and a NICAM VCR is so that you can listen
and watch a live NICAM transmission at the same time as you record another one
also in NICAM!

> I believe that true NICAM recorders (not the cheap one, which records the decoded signal using
>  normal analogue - the small print points out that the recorded sound is stereo
>  but NOT hi-fi) have different filters and can record the encoded NICAM 
>  subcarrier signal - ie the recording is effectively digital.
    
    Would such a device be VHS-compatible ? Or would the on-tape format
    have to be different ?
    
    Trevor

Does anyone know anything about the NICAM kit that maplin sell. No doubt not as good
as the arcam, but at only 130 pounds it might be worth trying.

As a more general question can you get good hi-fi from kits?....

Hi,

I have built the MAPLIN NICAM tuner.

It is based on the Toshiba chip set, and
comprises 4 PC boards, all of which are high quality, double sided glass fibre 
with plated thru' holes.

Wiring is minimal, comprising ribbon cable for DC control signals and screened
coax for signal lines.

It provides 16 preset channels with optional IR remote control. Outputs are
composite video and audio. UHF Tuner is a high quality unit using SAW filters -
it was noticably better that the tuner in my TV.

Sound quality is pretty good, but I would recommend not using the IR volume
control as it uses some op-amp circuitry which is not very hi-fi - and it
increases distortion measurably (0.01%)

Automatic switching between FM and NICAM sound is provided, with manual overide..
NICAM mode indication is provided (stereo, dual language mono), with push
button selection of special (ie non-stereo) modes.

Physically, it is a midi sized box of reasonable quality, but not up to the
standard of fininsh of commercial units. It requires an outboard regulted 12v
AC adapter.

To build it, you need have a decent soldering iron (preferable a 60W 
TEMPERATURE CONTROLLED iron (eg Weller TCP) with a fine bit, and you need to
know ho to weild it properly. Test equipment needed is only a multimeter, since
all the critical RF stuff in the UHF tuner is pre-aligned. There are a couple
of cores to set but these can be done by watching/listening to the FM sound and
video outputs on a TV or monitor. (you can feed the sound & video outputs back
into your VCR and then use a normal TV if yours doesn't have the right inputs)

If you want any more info, call me on 844-3293

Rgds, Dave

    Or you could have bought my Arcam Nicam Tuner when I was selling it last
    year, Peter...
    
    (Too late now - I've found a reuse for it!)
    
    Steve