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Show HN: Resonate – Low-latency, high-resolution spectral analysis (alexandrefrancois.org)

46 points by arjf ↗ HN
Last April I shared about my Resonate project here (https://news.ycombinator.com/item?id=43694157)

A lot has happened since: the work I presented in much more detail at last June's International Computer Music Conference (ICMC) got best paper award. I also gave a talk at the Audio Developer Conference in Bristol last November, the video is on YouTube).

This year's work, which I recently presented at this year's ICMC, starts with known techniques from the phase vocoder literature to build self-tuning filter banks that extract very efficiently the frequency components that are actually present in the input signal. Overview on the project website, more details in the papers, including applications to super-resolution spectrograms and re-synthesis experiments.

As many people have pointed out, none of the techniques I have used are new (some of them even have different names across different fields), but I haven't seen them applied together in this way, and to me the results are incredibly satisfying and sometimes look magical. See for example this demo: https://youtu.be/LasdoIJJkw8

Of course the best way to experience in person is through the free demo app: https://alexandrefrancois.org/Oscillators

Looking forward to feedback from the community!

19 comments

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bialamusic
I have such app for more than 4 years. Your algorithm is not new - it is new for you only :) Here is the app: https://play.google.com/store/apps/details?id=com.bialamusic...

https://apps.apple.com/us/app/chord-detector/id1495811175

arjf
Spectral analysis has indeed been around as a concept for centuries and there have been apps based on the FFT for decades, so definitely nothing new there. What I have implemented however, while based in known concepts and techniques, allows to achieve real-time, low latency and high resolution (both in time and frequency dimensions) performance that I believe are out of reach of established (published) methods. The apps you link are most likely making use of the FFT, which has become widely supported with efficient hardware acceleration and easy to use libraries, because of its central role in ubiquitous DSP applications, e.g. compression. I would be interested in any publications or at least technical descriptions of algorithms/systems that achieve similar performance!
bialamusic
No FFT in the showed apps. It is the very same algorithm you are trying to reinvent but adjusted for REAL world use by solving the REAL issues as accounting for natural harmonics and and balancing the resonator sensors output
jmpman
There are some piano tuners I've found who are a bit on the spectrum, who believe they can tune a piano in a way that no digital device can replicate. I'm skeptical, and would like to see how this method holds up against one of these savants.
arjf
A tracking resonator bank should self-tune to any frequencies... so as long as the density of resonators is adequate, after convergence, it should paint a representative picture of the tone profile. Then you can try funny chords, or see how harmonics interfere, or see what happens when you hit 2 adjacent keys, etc.

Fun analysis experiments like this are why I made the free demo app (it runs on iPhone/iPad/Mac):

https://alexandrefrancois.org/Oscillators/

jmpman
Check out the big brain on Brad....

Impressive. Thanks for the pointer.

jmpman
Why does it only go down to 32.70 Hz? I just learned that watermelon ripeness can be determined by the FFT of 17Hz. Tried thumping my phone on th watermelon with your app. No luck. Can you make it go lower? Or is this some fundamental limit of iPhone hardware?
arjf
32.7 Hz is C1, lowest C on a standard piano (A440 tuning).

No inherent limitation of the technique, the resonators can be tuned to much lower frequencies. But indeed you‘ll need a better mic than the iphone’s to get frequencies below 50Hz iirc… too bad - the watermelon ripeness checker could be a really cool app :-)

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jmpman
Side note, I was playing with your app on my piano, checking each key. I noticed that the lowest keys didn't actually have the lowest values in your app. Maybe I'm misunderstanding how the app works?
j-river
A useful demo for this kind of tool would be a side-by-side on difficult inputs: fast pitch bends, dense chords, and low-SNR recordings. Latency is easy to appreciate visually, but robustness under messy audio is what usually decides whether spectral tools become part of a workflow. Even a small set of repeatable test clips would make the tradeoff much clearer.
arjf
I think the output of a tracking resonator bank is only the basis for higher level analysis that will produce results suitable for specific applications (see my comment on frequency component tracking and prediction/feedback).
RossBencina
Nice. To the folks saying "nothing to see here" this appears to be a variation of filter-bank spectral analysis where each band varies in frequency to track "the" in-band sinusoid. Somewhat like a bank of PLLs each with its own tracking bandpass filter. By using IIR filters rather than FFTs you avoid the latency of buffering up a full frame of data before you can run the FFT analysis. I am curious how this handles input containing broadband transients. It might be interesting to use CIC filters rather than an IIR lowpass to get better time selectivity, but maybe that's already been addressed, I didn't read the papers.
_def
Slowed down higher pitch example was nice to hear, as this is where often conventional methods are heavily artifacted
deckar01
I don’t like the bins drifting from so far away so slowly. There needs to be repulsive force that prevents the bins from colliding.

It would be interesting if the resonators could adaptively model timbre to factor out harmonics while still handling unique timbre at each frequency. That could produce a pitch diagram color coded by instrument.

Edit: I bet you could fork a resonator and run over the window it just finished in reverse to correct the drift.

bialamusic
REMINDER! You can not put your name under something that is on the market since 2019 in several products with more that 100K users just because you wrote some paper in 2025! You may use it, you may describe it, you may try to improve it but you can not title yourself an inventor :) You are just late to this!

https://play.google.com/store/apps/details?id=com.bialamusic...

https://apps.apple.com/tn/app/chord-detector/id1495811175

https://apps.apple.com/us/app/resonance-chromatic-tuner/id16...

Also Siren's Chore effect and more...

bialamusic
Why the author is acting hostile ?? Here is description of my method for frequency detection using resonance sensors from 2019! https://bialamusic.com/resonance_frequency_detection/

If you want to cooperate - I am open for that and I can share more. But this is public knowledge and should stay that way. Why you are deleting my comments in youtube - I have apps with 100K+ installs using such method and I can share details if you are really interested