General question on Sigma's Hilbert Transform block

     Hello Jim,

     Just as you expect, the packaged Hilberts use 103 instructions each -- two would still use far less than one FIR.  Below I made a simple headphone effect with two Hilbert transforms, one active and one reference.  By adding a relative 90 degree phase it moves the sound image from inside your head to all around you.  Somewhere in EZ I have also posted a variable audio notch filter using SSB modulator / demod to shift the incoming audio (instead of moving the notch filter, which isn't possible on a ADAU1701 without external coefficient calculation).

     Best regards,

     Bob

Thanks for the vote of confidence, Bob, but we still need a Help/Wiki on that block.  Your movable notch sounds like a challenge, and I'll bet there's a way!

Your headphone 'ambience synthesizer' is a cute idea.  An interesting application is to run the audio from your ham rig through an 800Hz notch filter and then through the Hilbert device to stereo headphones.  But go back and recover the 800Hz by subtraction and add it to both L and R.  The effect is hash and noise all around you and the CW signal-of-interest right in the middle of your head.  Eerie, though I don't know if it helps Morse intelligibility since I never learned to copy it.

I have an article relevant to this you might find interesting, if I could figure out how to get it to you.

     Hi Jim,

     I found the EZ link to the variable notch filter using Hilbert-based frequency shifting:  https://ez.analog.com/dsp/sigmadsp/f/q-a/65699/audio-filtering-for-radio-communications-using-adau1700-1/91459#91459

     Thanks for offering the article.  The old Jive Software based Engineer Zone originally had a private message system but it was later disabled, presumably due to abuse.  The present Telligent version can do PMs but I don't know how.  If I'm not mistaken, we have to be "friends" of each other to send/receive PMs.  I have accepted several friend requests but to my knowledge have never received any private messages -- so I'm wondering if PM really works or else I have no idea how to access my PMs.

     Best regards,

     Bob

Hello, Bob.

I don't recall ever getting back to you on this subject after receiving this message, and humbly apologize, either if I did respond and forgot, or didn't.  And if I didn't I have put the "Phase Buster" project I did a write-up on in Dropbox.  If you are still interested you can read it here:
https://www.dropbox.com/s/nwvxm9jmj7gudbf/PhaseBuster%20aX%20Article.pdf?dl=0
...sorry it's such a big file.

As far as PMs, goes, only today I received one of those from a fellow in China who is attempting to develop an FM stereo encoder and has asked for help, not only from the group, but has addressed me directly, as he may well have done to you and others as well.  I explained that my firm developed several commercial products utilizing a very simple, yet successful stereocoder implementation in Sigma, but that I am hesitant to share a Sigma schematic with him for 'proprietary' reasons.  I did, nonetheless, give him some food for thought and hope he succeeds in surpassing his 35dB separation figure. 

Actually 35dB is darned good enough for normal stereo programming and, in fact, one of our competitors in the arena has implemented a dynamic means of limiting separation to lessen the effects of multipath.  I believe it was Bell Labs that demonstrated quite "...thrilling and believable stereophonic reproduction..." with just 6dB separation.  We're consistently getting 60dB from Sigma, which I am loathe to sabotage.

I hope all is well with you and will be looking for choice tidbits of wisdom from you in these august pages.

Best regards,
Jim Wood
INOVONICS, INC.

"Phase Buster" is neat and wonderfully analog!  I miss that stuff sometimes.

Thanks, KJB.  Your old and dear friend, analog, misses you and waits eternally and untiringly for your return with welcoming arms.  Never lose sight of the fact that we live in an analog world, and even large corporations with huge investments in digital technology are smart enough to keep the word Analog in their name, and support it with various Devices.