I don't understand the bit about it adding greater selectivity.
It is an audio filter, which applies after the radio has completed its work.
I cannot see how it would improve "selectivity" - it merely uses an
algorithm to reduce background noise. Are you using this term in a
relative manner, as in making the wanted signal easier to distinguish
from unwanted noise? If so, then it does that, but that is not how I
would describe its operation.
The value of the Timewave DSP 599zx depends upon what you expect from
it. It will reduce background noise, and the more aggressive you do
that, the more unwanted digital artifact and distortion will be
introduced.
I once used used the Timewave 599+ and now use a Timewave DSP-599zx with
all my HF receivers. I like it, and it is very useful- but one must
recognize it is not a cure for background noise and you may not want to
use it all the time.
What is good about it -
It DOES reduce random background noise and it can make a noisy signal
more readable. The auto notch ("Tone") button kills unwanted tones and
squeals and that, alone, can be a huge benefit. Faster and easier to
use than the notch filter on the rig. Instantly, gone.
It has high an low pass audio filters - you can tailor the audio as if
you had a two or three band equalizer - you can roll off the low and
high frequencies - I like to cut the audio between 250 Hz and 3000 Hz
which kills a lot of high pitch hiss and eliminates low pitch hum.
There is a low cut and high cut control, and it is easy to tune that on
the fly - far easier than working the rig menu and the adjusting the rig
settings. Also the rig settings are quasi-permanent, in that you have
to enter the rig menu to change them. In contrast, the knob on the DSP
filter is out front and always available and quickly, and easily,
adjusted, at least easier than accessing the rig's equalizer menu
settings. It has a few, not many, memories so you can have multiple
settings for different needs. I have a light, med, and heavy
(aggressive) filter settings, respectively.
I do do much with digital modes, but those who do like the DSP 599zx for
what it can do for those modes. I understand it really shines on the
digital
modes, whereas it use with SSB signals is less effective. But I like
mine on SSB work and would not sell or trade it at this point. Not a
cure, but sometimes a big help.
What is bad about it -
It DOES introduce some unwanted digital artifact and can distort the
signal if you over do it. Using this filter aggressively involves a
trade-off between noise reduction and signal distortion. Finding the
sweet spot is essential, but in a pinch, it can make the difference
between working a station or not. Also, it cannot cure all noise and
only provides a help. You want to avoid overloading it - easy to avoid,
but you do want to watch the little red light that tells you it is being
overloaded.
Bottom line -
Only you can decide if it is worth the cost. The DSP_599zx currently
available is, in my view, much better than the older model DXP-59+ I
used to have. I purchased the WestMountainRadio Clear-DSP unit at
Dayton, but have yet to try it out. I will likely do that soon. I
expect it will have less aggressive filtering effect, but also less
deleterious impact on the final audio. Time will tell as I work it on
line and try it.
That is MY take... anyway.
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