Petter wrote:
>
>Observe the change in topic...
>
In fact, there is a serious point behind my suggestion.
>
>"Ian White, G3SEK" skrev:
>> The world clearly needs a standard reference .wav file.
>>
>> Now who shall we nominate?
>
>Shall we take someone from Japan , deep Texas or even Wales ??
>
>No I think we need to define a dynamic test method that simulates the human
>voice.
Devising a test signal that adequately simulates the characteristics of
the human voice is extremely difficult - and even when you've done it,
it still suffers from the same problem of "whose voice are you
simulating?"
I think there could be two types of test - a simple tone-based one, and
a totally realistic test based on real voices. I just don't see much use
for the in-between cases using elaborately synthesized test signals,
because in the end it's performance with real voices that interests us.
1. I think we all agree that the classic two-tone test is too simplistic
because it doesn't exercise the power supply regulation in the way a
real voice does. So let's have a two-tone signal, with envelope
modulation of both tones at a swept frequency from say 1Hz up to several
hundred Hz. If you keep the separation of the first two tones constant,
their IMD products would stay in the same place on the spectrum analyser
screen. This allows you to see how each IMD product level varies with
modulation frequency.
2. But why bother with building up a more complex simulation of a human
voice when we can have the real thing - or indeed several human voices?
The idea for this test would be to set the spectrum analyser to peak-
hold mode and scan for a long time to build up a picture of the highest
IMD levels there have been at any frequency. If you choose the right
recorded material, you can use as many different voices as you have time
to run the test for, and keep building up the IMD picture.
The signal source for Test 1 could be built in hardware, but this seems
a waste of time when we have PCs with sound cards. Does anybody know how
to program a sound card to generate Test 1 - or even a basic two-tone
test with one tone out of each L/R channel?
The big development in recent years is that we can now create or record
tone and voice test signals, and copy them digitally with complete
accuracy all around the world.
>It has to have the frequency components of speach mixed with the freqency
>component
>of the syllable frequency.
>Another interesting thing is energy content of the different frequency
>components .
>
>The dynamic three tone test I mentioned in an earlier post is a step in that
>direction, it just have to be defined and agreed upon..
>
That would be a very good start... but before we do, we need to be sure
that we're not making an amateur attempt to re-create something the
professionals have been doing for years.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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