[[email protected]]

One topic often ignored, or at least often misunderstood, is the
received audio.
Simply put, the whole goal of receiving DX stations is to actually
understand
what is being said. Anything that degrades understanding degrades
reception.

First, there is no good substitute for having a professional hearing
test.
My speech pathologist friend agreed that out of the many that I found,
this one makes no claims and might spot "gross problems".
http://www.freehearingtest.com/test.shtml

The speech pathologist pointed out that "if your on line friends are
even half
way serious about listening to and understanding weak voices in a noise
environment, they really should have their hearing test by a
professional".
She pointed out that subtle hearing deficits can have a major effect on
one's
ability to understand. I have learned that the further an accent is
from the version
I hear every day, the stronger, as in better SN/N, the signal has to
be. And for
the foreign languages that I understand, even less noise is allowed.
Since I can't
do very much about the noise, I try to not degrade the received audio
any more
then I must.

From my perspective anything that degrade or distorts the received
signal simply
adds noise. And some of what I am saying appears to contradicts other
parts.
For instance I feel that under ideal conditions there should be no
bandwidth limits.
But I am a strong believer in Dallas Lankford's elliptical low pass
audio filters. And
I love narrow crystal filters for some situations.

Quoting form Kiwa's "Tips for Improving Receiver Performance",
http://www.kiwa.com/rxtips.html:

"All capacitors from the point of detection to the speaker output
should be examined.
All ceramic capacitors within the audio path (from disc to SMT types)
should be
replaced with a polyester type such as the Panasonic V or B series
(available from
Digi-Key) or WIMA MKS-3 types. Low pf values (less than 10,000pf) could
also be
replaced by polystyrene types (available from Mouser7). Ceramic
capacitors,
especially the general purpose disc capacitor types are notorius for
creating bad
audio. Probably the best description as to what they do to the audio is
that they
create a smearing sound which reduces the overall clarity to the audio
quality.
The polyester types are much more transparent and they will improve the
audio quality."


There have been several threads on the effects various capacitors types
have on audio.
Instead of reinventing the wheel I will offer some links to pages that
detail and display
these effects.
http://members.aol.com/sbench102/caps.html

Walt Jung has a very interesting group of very informative articles
regarding amplifiers.
And one especially useful pdf showing a "real time capacitor checker"
http://waltjung.org/PDFs/A_RealTime_Signal_Test_For_Capacitor_Quality.pdf


To be fair, Ron Elliot has another viewpoint.
http://sound.westhost.com/articles/capacitors.htm

Mr. Elliot has some fine designs and I love his simple MOFET power
follower.
Very clean and very simple.
http://sound.westhost.com/project83.htm
Mr. Elliot also has what he calls a "Sound Impairment Monitor"
http://sound.westhost.com/sim.htm
http://sound.westhost.com/project57.htm#top
I found his first unit to be very usefully in evaluating amplifiers and
amplifiers
that showed significant "difference" also degraded weak, poor S/N,
audio
signals. Hi unit also shows the effects different capacitors have on
audio.


Spoken language is made up of small pieces called phonemes.
Anything that causes phonemes to be misunderstood reduces
intelligibility.
Since most readers will speak English as their primary language, I will
use
English words for examples. Other languages will suffer from similar
effects,
though naturally the exact sources of confusion will vary from language
to
language.

It is important to realize that even if you can not tell sailing from
failing due
to audio defects, you can often get at least the gist of a conversation
from
context.

These are links to interesting information about audio intelligibility.
I used a similar set of words to those in the first three links.
While these were designed for sound reinforcement studios, they were
the best I could find and have been very useful in my ongoing quest
for improved reception.

http://www.meyersound.com/support/pa...ch/drtlist.htm
http://www.meyersound.com/support/pa...ech/pblist.htm
http://www.meyersound.com/support/pa...ch/mrtlist.htm
http://www.meyersound.com/support/pa...h/section3.htm
http://www.meyersound.com/support/pa...eech/appen.htm
http://www.meyersound.com/support/pa...ossary.htm#drt

"Communications and speech intelligibility"
http://www.isvr.co.uk/spe_hear/comint.htm

Thoughts on "HiFi" SSB,
"What is Lo-Fi - Mid-Fi - Hi-Fi and Extended SSB ( ESSB ) ?"
http://www.icycolors.com/nu9n/essb.html

"The Effect of Bandwidth on Intelligibility"
http://www.icycolors.com/nu9n/images/Sound.pdf

This is a quote from
http://www.meyersound.com/support/papers/speech/section2.htm:

"One of the most obvious aspects of sound system performance that
affect intelligibility
is frequency response. Severely band-limited systems deliver speech
poorly. For instance,
telephones are generally limited to a 2 kHz bandwidth, and this makes
it hard to distinguish
between "f" and "s" or "d" and "t" sounds."

This is a link to charts that show the effect of increasing noise to
intelligibility.
http://www.meyersound.com/support/papers/speech/mbn.htm
http://www.meyersound.com/support/papers/speech/mf.htm

And this chart is usefully in that it shows the effect of a
"competing", and
unwanted, interfering voice(s).
http://www.meyersound.com/support/papers/speech/mv.htm

Little things can matter a lot more then I would have believed 18
months ago.

With every minor improvement I have made in my system, there has been a
direct and corresponding increase in my ability to understand weaker
and
weaker signals. This is more then just my opinion, it is the result of
careful
measurements, over a 12 month period using the ISM/HiFer beacon that
I have already mentioned.

I hope some find this useful.

Terry

[Guy Atkins]

Terry,

A big AMEN to everything you've said about the importance of audio quality
in DXing and receiver characteristics. This is one of the key areas in any
receiver I consider. If it doesn't provide high-grade audio out of the box,
I will look at mods for audio quality that my friend Craig at Kiwa
Electronics proposed. He first helped me out with an ICOM ICR-70 in the
1980s, and later I saw (heard!) what he could really do with audio quality
when designing equipment from the ground-up (ie, the Kiwa "MAP" unit).

The clean, low distortion audio from the SDR-1000 is one of the reasons it's
my main receiver. In a listening environment like the Pacific NW where there
is less thunderstorm static, particularly at sunrise with a Beverage antenna
at the coast, a quiet receiver can REALLY reveal the weak signals at the
noise floor.

Fortunately, the manufacturers have come a long ways with audio quality
since the days of the "wooly" JRC NRD-515 and the excessively bassy response
of the stock ICOM ICR-70. More often than not, the current rigs have far
better audio than communications receivers from the 1980s and 1990s.

Guy Atkins
Puyallup, WA
www.sdr-1000.blogspot.com


wrote in message
ups.com...
One topic often ignored, or at least often misunderstood, is the
received audio.
Simply put, the whole goal of receiving DX stations is to actually
understand
what is being said. Anything that degrades understanding degrades
reception.
SNIP

[Tom]

wrote:
First, there is no good substitute for having a professional hearing
test.
My speech pathologist friend agreed that out of the many that I found,
this one makes no claims and might spot "gross problems".
http://www.freehearingtest.com/test.shtml

Great collection of references, Terry. I have to endorse the above
statement from recent experience with my new FT-817ND. Right from the
outset, I detected a raspy distortion on CW and SSB, and later on
detected a more subtle level of it on AM. The FT-817 does not have AM
synch but you can use it very effectively in unsychronised ECSS mode by
tuning an AM station using LSB or USB - the carrier is well enough
filtered that even though the tuning steps are 10 Hz, the zero beat
error is not strong. However, I relaised that the raspy distortion was
being turned on and off or was being modulated by the zero beat error.

Went back to the dealer and found their demo unit has the same
distortion. Searched the Yahoo group and found sporadic references of
others detecting this distortion. Posted a message about it and a poll
and was surprised by the range of responses, especially after I have
formed the conclusion that it is a design fault. The vast majority of
respondents do not detect the distortion, even after I posted a sample
A-B comparison of FT-817 received audio with and without the raspiness.
By backing off on RF gain so that the signal strength falls below the
AGC threshold, the distortion rapidly diminishes; it appears to be at
its worst just at and a little above AGC threshold and eases a little
with stronger signals. Even QRN can trigger the AGC and as a result the
noise is distorted and worse than it would be through a linear system.

This distortion looks to be mainly harmonic and at its worst is about
1%THD - doesn't look like much but it sounds worse! Perhaps because the
harmonics are all of similar amplitude. When simulating a distorted CW
signal using a multitone generator, the addition of the fifth harmonic
had a pronounced effect.

If I'm right that it is a design fault, then it would appear that many
of the respondents who said that their FT-817 does not exhibit the
problem must have faulty hearing or a faulty monitoring system.
Certainly, passing a CW (or for that matter, any) signal through a low
pass filter will suppress harmonics of a high enough fundamental
frequency and have a mitigating effect. This would be most pronounced
on CW because harmonics of bass speech spectrum and of QRN will still
fall within the passband.

I very much want to fix the problem but continued warranty coverage
and tiny SMD's are rather large barriers. And so far, Yaesu has not
allowed anything more than that this may be "more or less nominal for
this radio"!

73, Tom

[Telamon]

In article . com,
"Tom" wrote:


I very much want to fix the problem but continued warranty coverage
and tiny SMD's are rather large barriers. And so far, Yaesu has not
allowed anything more than that this may be "more or less nominal for
this radio"!

Use a 10 X magnification like I do. You can buy binocular scopes that
mount on the bench or you can wear the head gear then those small SMT
components will not be a problem down to 0402 size.

--
Telamon
Ventura, California