[TenTec] Omni VI+ the best and other great radios

[Dr. Gerald N. Johnson]

On Sat, 2010-01-30 at 13:48 -0500, Richards wrote:
> 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.

I call a 25 Hz brick walled bandpass, SELECTIVITY! Whether at audio or
IF or RF it still sets the spectrum limit on what I'm going to hear.
Remember in the SSB receiver all it does is translate a section of RF
spectrum to audio, it doesn't demodulate. So selectivity is effective at
any stage of the process. Unfortunately with the outboard audio filter
its after the AGC detector so keyed unwanted signals will affect the
receiver output even when you don't hear them through the audio filter.
One of the limitations of the technique.
> 
> 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.

That is to say when reducing white noise the residual doesn't sound like
white noise anymore. And that limits further processing by the
experienced ear.
> 
> 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.

But really hard on CW signals!
> 
> 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.
> 
> ====================  K8JHR  ==============================
> 
There are many noise reduction algorithms about. Some act like
selectivity, some average out random noise, others the vendors won't
admit how they work.

73, Jerry, K0CQ