Audio phase shift circuit design wanted. - Page 1
Forum section: electronics / projects

author: Jim-0000
author_rank: Regular Contributor
timestamp: July 10, 2019, 11:16:48 am
content: I understand a variable delay filter can be built around a NTE1641 or a 2399 chip.If someone can suggest a circuit or a link to a page that might have one, I would much appreciate it..Jim.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: July 10, 2019, 11:38:06 am
content: PT2399 is pretty straight forward, datasheet features basic schematics for echo and delay applications.Also:http://www.diyaudiocircuits.com/tutorials/pt2399-digital-delay-analog-echo/

author: ledtester
author_rank: Super Contributor
timestamp: July 10, 2019, 11:52:36 am
content: Supposedly the NTE1641 is a replacement for the MN3007:https://www.diystompboxes.com/smfforum/index.php?topic=48790.0In the datasheet for the MN3007 there is an example application circuit:http://www.kazumi-kikou.com/pdf/3007.pdfThe example circuit employs a MN3101 as a "BBD clock generator". This thread suggest that more common CMOS logic chips can be used to replace the functionality of a MN3101:https://www.diystompboxes.com/smfforum/index.php?topic=72447.0

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 10, 2019, 12:03:27 pm
content: Just nitpicking here, but strictly speaking, a fixed delay will only give a fixed phase shift at one specific frequency. So you have to make sure a delay is what you really need.

author: Jim-0000
author_rank: Regular Contributor
timestamp: July 10, 2019, 01:01:26 pm
content: Quote from: SiliconWizard on July 10, 2019, 12:03:27 pmGood point and you are right, a delay may not work for what I want.I want to invert the phase of perceived (or actually heard) frequency of a Tinnitus sufferer.So, the phase shift (of 180 deg) will need to be adjustable for any frequency over the audible spectrum.Alternative suggestions most welcome.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 10, 2019, 02:22:42 pm
content: Quote from: Jim-0000 on July 10, 2019, 01:01:26 pmI'm no doctor, but I don't think applying a real sound will counteract the perceived sound of tinnitus; the latter is a phantom sound that may or may not even be the result of a signal on the auditory nerve (ie - it could be generated in the brain, so truly imaginary). Even if there is a signal on the auditory nerve how would you cancel it out without painstaking scanning of frequency and phase to find the null? This just doesn't seem at all practical to me.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 10, 2019, 02:32:29 pm
content: Agreed. Some cases of tinnitus can be objectively measured with a microphone inside the ear canal (otoacoustic emissions), but AFAIK, the more common cases are "phantom sounds" as MagicSmoker said and can't be related to anything acoustic. Trying to "counter-act" them on a phase-reversal basis would not make any sense, and estimating the average frequency (es) of tinnitus (unless again they are otoacoustic emissions) is a very tedious and error-prone process.If, again, you're only interested in otoacoustic emissions, I would still not know how you could "cancel" them out as the measured signal inside the ear canal may have no useful direct phase relationship with the emissions themselves (which are due to the outter hair cells...)

author: IDEngineer
author_rank: Super Contributor
timestamp: July 10, 2019, 03:59:41 pm
content: This is a fascinating idea.It makes sense that the "source" of the (possibly phantom) sound could be anywhere in the signal chain, from actual stimulation in the cochlea to processing errors in the brain itself. But regardless of the "source", the real question is how would the brain interpret the superposition of a cancelling signal? We understand that acoustic mixing could cancel an actual sound at the eardrum... but electrical cancellation is also a real thing, and once a "signal" makes it to the brain why would the brain magically interpret two different signals differently? So what if one started out as "real" (externally acoustic) while the other started out as "fake" (undesirable stimulation of the cochlea, or even a flaw within the brain). Once both "signals" are within the auditory processing centers they are just that - signals - and aren't tagged as "real" and "fake".Yes, syncing up the frequency and phase could be challenging. But I'll venture out on this limb a ways with another idea: Biofeedback. There are countless examples of the brain adapting to accommodate things. Some are natural (did you know that each person's neural network is unique, and that an infant's brain learns to map theirs?) while others are external/artificial (such as learning to modulate one's own heartbeat and blood pressure). I wonder if a closed loop system could be created whereby the brain modulates the frequency and phase to minimize the effect of tinnitus. There's an obvious error signal available, and an obvious result of improved control available, so in theory it's possible. Might take time but so does learning to walk with a prosthetic that is controlled by nerve impulses.Again, a fascinating idea.

author: Audioguru
author_rank: Super Contributor
timestamp: July 10, 2019, 04:20:53 pm
content: To cancel a sound you need a few accurate things:1) The exact frequency.2) The exact amplitude.3) The exact waveform (including all the harmonics).4) The exact phase shift.Who says with tinnitus they always stay the same?EDIT: At times you might end upincreasingthe level of the sound.

author: Audioguru
author_rank: Super Contributor
timestamp: July 10, 2019, 04:33:09 pm
content: Thinking about tinnitus, I always hear faint very high audio frequencies. Their frequency and amplitude are random. Try to match that!

author: magic
author_rank: Super Contributor
timestamp: July 11, 2019, 08:28:31 am
content: Quote from: Jim-0000 on July 10, 2019, 01:01:26 pmThen you simply want an inverting opamp stage.But as others pointed out, you can't cancel a signal that you can't measure in real time.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 11, 2019, 01:19:48 pm
content: What are still commonly used as a way of relief for tinnitus are masking signals. They are often some kind of broadband noise, such as filtered and/or modulated white noise.For those interested in knowing a bit more:http://www.tinnitusjournal.com/articles/use-of-masking-for-tinnitus.pdf(https://www.tinnitus123.com/tinnitus-maskers/)

author: ogden
author_rank: Super Contributor
timestamp: July 11, 2019, 02:20:03 pm
content: Quote from: Jim-0000 on July 10, 2019, 01:01:26 pm180 degree phase shift for any frequency or just broadband noise is simple DSP task - invert polarity of waveform/signal. Problem in your case is - you do not have waveform nor signal to invert. Basically your idea of creating 180-degree phase shifted sound to cancel Tinnitus sufferer is impossible. If you say that it is possible then why don't you earn money winning lotteries and trading stocks? Audiogury pretty muchexplainedwhy (it is not possible).

author: Audioguru
author_rank: Super Contributor
timestamp: July 11, 2019, 02:39:48 pm
content: I hate to hear acid rock or Rap because they are broadband noise. Instead of hearing noise to mask tinnitus then maybe good music would be better.

author: Jim-0000
author_rank: Regular Contributor
timestamp: July 11, 2019, 11:53:26 pm
content: Quote from: SiliconWizard on July 11, 2019, 01:19:48 pmThanks for the reply. I will read the link. More later.Jim.