[Elecraft] Re: Binaural CW Reception

Thu May 25 16:04:22 EDT 2006

For those who might be interested: Kanga US sells a kit for a stand alone binaural receiver:

http://www.bright.net/~kanga/kanga/KK7B/biqr.htm

This is not an endorsement of any kind, and I am not affiliated with Kanga US. 

The page is interesting though, because it contains a link to the original QST article describing the receiver.

73,
Mike

----- Original Message -----
From: Jerry Volpe <kg6tt at arrl.net>
Date: Thursday, May 25, 2006 2:35 pm
Subject: [Elecraft] Re: Binaural CW Reception

> I have done a couple of Binaural CW reception projects and found the
> results very appealing. Let me begin  by sharing a few thoughts:
> 
> 1. With binaural reception you normally would NOT use tight CW
> bandwidths as the object is to allow more audible information to
> be processed by our brain. I think that you would want at least 
> 600Hz or
> greater. I typically use a 1000Hz type filter or wider but generally
> nothing tighter. A stereo 'soundscape' is created within your head 
> withthe primary signal (the one centered in the Binaural filter) 
> appearingin the center of your head, and the ones higher in pitch 
> progressivelyoff to one side and the ones lower in pitch off to the 
> other side.
> 2. Due to the sound dividing by frequency you notice only the lower
> frequency background 'noise' component in one ear and the higher
> frequency component in the other. It is surprising how much LESS in
> intensity the noise is overall than what it was with combined 
> energy to
> both ears. This alone is worth the price of admission.
> 3. Many of today's CW operators have not trained themselves to use 
> theirown brain as a CW filter and instead rely on very sharp band-pass
> filters for single-signal reception. Binaural CW reception provides
> multiple signals which many find too confusing.
> 4. Binaural CW reception should be great for NET, roundtable, and even
> contesting where you often need to hear many stations on slightly
> different frequencies.
> 
> My first project was a stand-alone Binaural CW filter using a pair 
> of OP
> Amp ICs. Basically, the audio input passed into both a low pass filter
> and a high pass filter with the low and high frequency cutoffs at the
> desired center frequency.... 700 Hz for example. The output of the 
> eachfilter was further amplified (as needed) and then applied to 
> eitherstereo speakers or to stereo headphones.
> PRO: Small package. Simple approach. Low cost. Easy to build. Works 
> wellenough for a single design cross-over frequency.
> CON: I could have used better quality OP Amps for lower distortion. 
> Theones I got were from Radio Shack (sigh). Still not bad. Can't 
> changecross-over frequency. This is OK if your receiver has a fixed 
> CW offset.
> Myself, I like to change my offset to minimize long term listening
> fatigue. But then again only a couple of my transceivers allow for
> that.... most don't. Another CON was the fact that I had to build this
> filter. It was amazing to me how many hams were interested in the
> project (I posted the info on the Ten-Tec reflector last year) but 
> wereunwilling or unable to assemble a project without a kit.
> 
> I think it would be wise to use two pass-band filters rather than a
> low-pass and a high-pass configuration. That way you can also take 
> awaythe unnecessary lows... say below 300 Hz and the unnecessary highs
> perhaps over 1500 Hz. These filters should not have sharp slopes as 
> thatwill add ringing.
> 
> My second project began with the following in mind:
> 1. Using band-pass filters rather than low-pass and high-pass.
> 2. Include the ability to move the combined filter cross-over for
> different CW offsets.
> 3. Get the lowest distortion possible in the filtering.
> 4. Use something commercially available rather than 'build your own'.
> 
> My first thought was to obtain two SCAF audio filters (highly
> programmable as far as band-pass characteristics, no ringing, low
> distortion). SCAF filters are not too expensive (you need two) when
> found used. I have seen them sell for around $40 to $60 each. However,
> before I found the two filters I decided t use another approach 
> using a
> 62-band, two channel, Pro Audio equalizer. The one I obtained (for $65
> used!!!) was a practically new Crate LS3-231. With this approach I can
> move my cross-over frequency as desired and have good control of the
> high and low frequency roll-offs. Distortion is negligible. I would 
> notrecommend this approach with a typical home stereo equalizer as the
> filter quality is not good..... the band separation is poor.... and 
> youdon't typically have near enough bands (the Crate has 1/3 octave 
> bands)to allow selection of the appropriate cross-over 
> frequency.... and I
> doubt they hold up well in a high RF environment. Anyway, I am 
> currentlyusing the Crate solution and it does a great job. Trouble 
> is I want to
> use this equalizer for other types of reception so I am continually
> reprogramming it. For that reason, and for a bit better cross-over
> programmability, I am still planning the simpler approach using two 
> SCAFfilters (as soon as I find what I am looking for at a price I 
> want to pay).
> 
> About DSP filters in this application:
> 
> I know of one commercial manufacture, TimeWave, that includes Binaural
> CW reception in their high end DSP filter. I had my suspicions 
> regardingDSP signal path delays and QSK CW operations. I obtained a 
> TimeWaveDSP599zx and found that the resultant binaural audio was 
> very good but
> that the delay was as bad as I had anticipated and unacceptable for 
> QSKover about 15 wpm. Your mileage may vary. :)  Anyway, if you 
> don't use
> QSK or you are very casual at speed and you don't mind spending a
> sizable sum for one of these filters go for it. Please note that the
> actual firmware version in the DSP-599zx is important and that only 
> themost recent firmware's have the Binaural CW function (or so I 
> was told).
> 
> Lastly, I do know that there are at least one current amateur radio
> transceiver with binaural CW reception built in.... perhaps more than
> one. I am talking a fairly expensive transceiver (not named) so for me
> it wasn't a reasonable path to just for this extra capability when I
> would make or configure binaural reception for a lot, lot less. Try
> before you buy!
> 
> 73,
> Jerry, KG6TT
> Fairfield, CA
> 
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