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Show HN: I made a free app to calibrate your turntable by simply playing a song

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Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#231

Post by davidmurdoch »

okatbest wrote: post #228
davidmurdoch wrote: post #219

Earlier quoted context omitted.

Usually when an app comes out on iPhone but not Android the excuse is that "Android users don't pay for apps so it wasn't a priority", despite it being way more difficult and a bit more expensive to develop for iPhone over Android. But in your case you don't plan on monetizing, so why iPhone first?

Well I have been developing native apps for both for over a decade, and I don't think either is particularly more difficult than the other. What it came down to is that I use an iPhone as my daily driver, and when I pulled my Android test device out of a drawer the battery was twice the size so I immediately brought it to an electronics recycling center. Which means that in order to complete the Android version, I ne…

Makes sense to develop for what you use yourself.

I've developed for both as well and would say getting _started_ with iOS development is about 10x more time consuming and complicated than Android -- or at least it was about 8 years ago.

I know you know this, but you don't need to own an Android phone to develop for Android (and you don't have to spend anywhere near $400 on one if you do want one).

Looks like it'll be a pretty great app and hope you do manage to get the Android version up and running.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#232

Post by hluska »

GauntletWizard wrote: post #194
hluska wrote: post #167

Earlier quoted context omitted.

I’m not sure about this. Thriller (by Michael Jackson) is one of the biggest pop songs of all time. It was also the fourth track on the A side. Bohemian Rhapsody (another one of the best selling singles of all time) was the fourth track on the B side. Those are two examples off the top of my head. If you give me a bit of time to put my kid to bed, I’m sure that I’ll find many more.

What you've just learned is that pop producers are not in tune with what's good. It's a hard lesson to learn.

Not really. I found data that shows that released singles aren’t necessarily placed first on a side.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#233

Post by khill »

cjk wrote: post #193
taylodl wrote: post #83

Earlier quoted context omitted.

Correct. That was often done when mastering with tape. Record at one speed, playback at another to make it sound more "lively." There are songs that were sped up that way anywhere from 25 to 40 cents. It's another reason why live music so often doesn't sound like the recording. When using digital mastering, you can also adjust the playback speed, but you can correct the shift. You get more "liveliness" without the sh…

A bunch of the High Voltage-era AC/DC stuff was this way, IIRC. It's really awkward to play guitar along with the songs in question unless you painstakingly match the goofy tuning of the song, or adjust the pitch of the song first.

Same with This Charming Man by The Smiths and Mary Jane's Last Dance by Tom Petty

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#234

Post by rerdavies »

crazygringo wrote: post #225
jerf wrote: post #217

Earlier quoted context omitted.

I am 100% abundantly positive that signal processing code could do this, and in fact by signal processing standards it's not even particularly hard. You may need more time than the app takes, though I am inclined to think that the app doesn't exactly need a number to twelve significant digits and you could get a single-digit-percentage significant digit lock pretty quickly. Even at 33&1/3rd you only need a few second…

> Now, scaling it down to where you can't hear it anymore may make it harder to believe, but the same code will pick it up. That's where you're wrong. FFT frequency bands are surprisingly wide. You can make them narrower but with the tradeoff of losing temporal resolution. And it gets worse the lower the frequency gets. There is absolutely no way you're going to detect a near-0.555 hZ effect from a few seconds of aud…

There are various DFT-based algorithms for high-precision pitch detection.

Two common algorithms are cepstrum and analysis, and auto-correlation, which involve taking the DFT or inverse DFT of the absolute value of the DFT of the signal.

Find the peaks of the result, and then fit a cubic polynomial to the the peak, and the bins on either side, and then calculate the maximum value of the polynomial. The value at the which the maximum occurs determines the inverse frequency, which can then be converted to pitch.

Both algorithms produce results that are accurate to less than 0.1 cents. You do have to tweak buffer sizes and windowing depending on what pitch ranges you are interested in, and do some post filtering to skip over transients.

The temporal resolution problem is solved by calculating the result on overlapping frames. .

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#235

Post by fmj »

CoffeeOnWrite wrote: post #177
fmj wrote: post #144

Earlier quoted context omitted.

My MK2 was off by about 3% when the pitch adjust was in the detent. To be fair, it had a rough life before it ended up in my hands. If you have a frequency counter they're pretty easy to calibrate the correct way though.

Did the delta show up on the strobe? Or is issue that the quartz is off and it’s feeding both the motor and the strobe? (Sorry if this is a dumb question. I don’t recall seeing speed calibration in the mk2 manual when I was setting up my secondhand decks)

I honestly can't remember if it showed up in the strobe or not, this was a few years ago. This procedure wouldn't be listed in the regular manual. It involves opening it up to adjust an internal potentiometer, and can't be reliably done without a frequency counter (I guess you could do it through trial and error, but it would take forever having to reassemble it and play a test disc after every adjustment,) so it is only in the service manual. You should be able to find a scan pretty easily though. Can't remember what frequency you need to hit, but it's low. If you don't have a proper frequency counter an Arduino will work just fine.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#236

Post by crazygringo »

rerdavies wrote: post #234
crazygringo wrote: post #225

Earlier quoted context omitted.

> Now, scaling it down to where you can't hear it anymore may make it harder to believe, but the same code will pick it up. That's where you're wrong. FFT frequency bands are surprisingly wide. You can make them narrower but with the tradeoff of losing temporal resolution. And it gets worse the lower the frequency gets. There is absolutely no way you're going to detect a near-0.555 hZ effect from a few seconds of aud…

There are various DFT-based algorithms for high-precision pitch detection. Two common algorithms are cepstrum and analysis, and auto-correlation, which involve taking the DFT or inverse DFT of the absolute value of the DFT of the signal. Find the peaks of the result, and then fit a cubic polynomial to the the peak, and the bins on either side, and then calculate the maximum value of the polynomial. The value at the w…

Sure but the problem remains: you can't do that with only a few oscillations of a weak signal against a loud noisy complex signal.

You simply can't detect an inaudible-to-human-ears 0.5 hZ signal from 3 or 5 seconds of complex normal-volume audio, down to the accuracy of cents, much less 0.1 cents.

As I said above: a 1,000 hZ signal? Absolutely. But a 0.5 hZ signal? Absolutely not. There just isn't enough signal for that level of precision. No matter what tool you're using.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#238

Post by cjk »

khill wrote: post #233
cjk wrote: post #193

Earlier quoted context omitted.

A bunch of the High Voltage-era AC/DC stuff was this way, IIRC. It's really awkward to play guitar along with the songs in question unless you painstakingly match the goofy tuning of the song, or adjust the pitch of the song first.

Same with This Charming Man by The Smiths and Mary Jane's Last Dance by Tom Petty

Oh man. Love Tom Petty. RIP.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#239

Post by rerdavies »

crazygringo wrote: post #236
rerdavies wrote: post #234

Earlier quoted context omitted.

There are various DFT-based algorithms for high-precision pitch detection. Two common algorithms are cepstrum and analysis, and auto-correlation, which involve taking the DFT or inverse DFT of the absolute value of the DFT of the signal. Find the peaks of the result, and then fit a cubic polynomial to the the peak, and the bins on either side, and then calculate the maximum value of the polynomial. The value at the w…

Sure but the problem remains: you can't do that with only a few oscillations of a weak signal against a loud noisy complex signal. You simply can't detect an inaudible-to-human-ears 0.5 hZ signal from 3 or 5 seconds of complex normal-volume audio, down to the accuracy of cents, much less 0.1 cents. As I said above: a 1,000 hZ signal? Absolutely. But a 0.5 hZ signal? Absolutely not. There just isn't enough signal for…

But you could easily detect frequency modulation of a 220Hz signal by a 0.5 Hz sin wave, which would have sidebands separated by 4 cents. This is conceptually similar to heterodyning. Wow in the source material ends up creating sidebands of the source material in a frequency range that is more amenable to signal analysis. Whether this works or not depends on how much wow an actually record player has. But a back-of-the-envelope calculation seems to suggest that very tiny amounts of wow should create detectable side-bands.

My suspicion is that OP assumed that the source material was accurately tuned to A=440, which is not a safe assumption, but is probably true for any source material that has a keyboard instrument which will almost always be tuned to A=440. Calculate the reference pitch for the source material, and you can tell how much the speed of the turntable is off. (And as others have pointed out, may be completely buggered by common mastering practices, and by Original Instrument recordings of classical music using pitch references other than A=440).

But it doesn't seem implausible that you could use analysis of wow in the source signal too.

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