EMRFD Message Archive 2482
Message Date From Subject 2482 2008-12-09 18:18:47 Rick Binaural Radio Many people have experimented with various binaural radio modes over the years. USB
and LSB Stereo techniques are common topics of discussion among experimenters, and
are closely related to several of the AM Stereo techniques popular in the US two decades
ago. Little has been written about all these experiments, perhaps because most
experimenters have discovered that it's difficult to describe what you hear to someone
who hasn't also experimented with binaural radio.
It takes some work to build a binaural receiver, either binaural IQ as in recent ARRL
Handbooks or a pair of phase matched receivers with two antenna inputs, as I described in
the Central States VHF Society Proceedings in 1984 and IEEE Antennas and Propagation a
few years later. It's a big enough task that I don't accept Farhan's claim of laziness, hi.
I've only built a half dozen different binaural receivers over the past 25 years, and I've built
many more conventional receivers.
Each time I try a different approach to a binaural receiver, I discover that I can hear things
I didn't even suspect existed about the most fundamental aspects of radio.
Two topics I can address are whether binaural has more impact on CW or SSB, and the
phenomenon of sound appearing to come from behind the listener in binaural audio
First the binaural audio "off-EMRFD" topic. The best way to make a binaural recording is
with tiny electret microphones down inside your own ears. I did some experiments in
1979, after discussions and demonstrations from some acoustics researchers who were
playing with the technique. When a recording is made using tiny microphones down
inside your own ears, and then played back through open-air headphones, the acoustic
imaging is uncanny. It is world apart from binaural recordings made using a Sennheiser
head or someone else's ears.
It is common when listening to someone else's binaural recordings for the sound to appear
to come from behind the listener, even though you know it was really in front. The
localization cues seem to be subtle, and once the brain makes a decision where the sound
is coming from, the mental signal processing seems to kick in to reinforce that position
and create a three-dimensional sound space. But when listening to recordings made with
your own ears, it's not just mental signal processing. You were there when the original
recording was made so your visual memory also kicks in. It is quite mind boggling.
Putting little things into our ear canals is one of the things our mothers warned us about,
and explains the popularity of foam heads with fake ears. I have one of those as well, and
use it occasionally. But for unbelievable results, there is no substitute for using your own
Now back on topic for the other question. Both CW and SSB use the receiver in "linear
translator" mode, where a selected passband is translated from RF down to the audio
range where we can hear it. If we use two channels and arrange somehow for them to
capture two different samples of the RF spectrum containing the same signal, then our
ear-brain perceives that as space. Whether that space contains CW, SSB, ionospheric
static, or just two uncorrelated channels of internal receiver noise is beside the point. It is
the space that matters. If there are multiple signals, receiver noise, local static, and
ionospheric noise, your ears can sort them out. It is a different way of listening, and the
most interesting part is not how the desired CW or SSB signal sounds, it is how the rest of
the space sounds.
I have had many visitors to my shack who have listened to my various binaural receivers. I
always include a binaural-mono switch on the front panel so that the listener can switch
between modes. Never in 25 years have I encountered anyone who preferred the switch
in the mono position.
I won't try to describe any advantages of binaural receivers. It is simply a different way of
listening. Every four or five years I get the urge to try a new set of experiments, and
spend a year developing a new receiver I can plug my stereo headphones into. Each time I
discover things I didn't suspect, and I've been playing this game for a long, long time. As
always on this group, I encourage doing experiments and then discussing results.
Have fun with the experiments, and Best Regards,
2483 2008-12-09 22:17:48 Stephen Wandling Re: Binaural Radio Rick,
Thanks for the great background info on this interesting topic. Below,
you have confirmed my suspicion of why we heard the 'barber' behind us.
My guess was: because that is where I would expect a barber to be;
either behind or beside me. Maybe a recording of a 'dentist' or
"bartender" would have them seem to be in front?
I'm trying to recall where and when I experienced listening to CW on a
binaural system. It may have been a recording. But, I recall things
like one signal being "to the right or left" of another, or a bit
"further away" from me. My recollection is that I could "see" the signals.
> It is common when listening to someone else's binaural recordings for the sound to appear to come from behind the listener, even though you know it was really in front. The localization cues seem to be subtle, and once the brain makes a decision where the sound is coming from, the mental signal processing seems to kick in to reinforce that position and create a three-dimensional sound space.
2485 2008-12-10 15:29:57 David Packard Binaural Radio Rick, thank you for the comments on binaural receivers. I have been
interested in the topic for a long time. I was intending to purchase
your binaural receiver kit, before the Kanga mishap. Will they be
available again? Have you published any of your binaural experiments?
They sound intriguing.
72/73, Dave K1YHR.
2488 2008-12-10 22:57:15 leon Heller Re: Binaural Radio ----- Original Message -----
2489 2008-12-11 11:58:45 Gary Johnson Binaural Radio I'm currently using a modified R2Pro with a binaural option, where the audio filters and final
gain are duplicated for the second channel. With simple switching, I get the option of regular
mono sound. Binaural is great for cruising the band and the fidelity is outstanding.
Another sort-of binaural audio processing method uses a HPF/LPF crossover where you send
high freqs into one ear and lows into the other. It's really for CW, and the crossover freq
would be at your favorite pitch, such as 600 Hz. I like it because you can use an SSB filter on
the receiver which generally sounds better, and at the same time you use your brain's spatial
ability to place a panoramic view of the audio spectrum right inside your head. Fourth-order
Butterworth filters seem adequate, but I've never tried other types. I vaguely remember some
early articles on this, maybe in QST in the 1970s.
2535 2008-12-30 09:29:05 davidpnewkirk Re: Binaural Radio 2548 2008-12-30 12:36:15 Rick Re: Binaural Radio Hi Dave,
Nice to hear from you. I designed and built a locked carrier
synchronous ISB receiver for my own experiments. The USB and LSB
channels are wide open, matched to within 0.1 dB and flat, using a
phasing technique. It is everything you say. I've wanted one since
reading a reference to the technique in Pat Hawker's Technical Topics
while in college.
Here in the Northwest US we are blessed with both strong and eclectic
shortwave programming from Asia and a largely polyglot population. I
frequently listen to a World Music program out of China in the
mornings in "Ionospheric Stereo." I find the USB-LSB frequency
diversity effects to be very musical. I've tried AB comparisons with
other AM receivers, including the excellent synchronous detector in
the Racal 6790/gm, and there is just no comparison. ISB stereo with a
locked carrier is in a class by itself.
Your comment regarding summing the sidebands with sync detection is
true as long as the carrier phase doesn't wander to 90 degrees
out--then one recovers only the distortion products. This may be
avoided by careful design of the synchronous detector, or by using
stereo ISB. It doesn't matter that the original program was
transmitted in mono, by the time it has passed through the ionospheric
concert hall, it has very natural-sounding stereo separation.
This would be seriously off-topic on an Amateur Radio discussi
2557 2009-01-01 09:25:41 davidpnewkirk Re: Binaural Radio (and injection-locked oscillators)