How does the freeze function work?

David Kissam

Does the indicator freeze function display the average pitch over a certain time window or the "instantaneous" pitch at some point in time after the note's attack? Another way to ask this is: does the freeze duration set the length of a measurement window or the length of a delay after the note's attack?

I know that there is no such thing as "instantaneous" pitch, as all measurements of frequency require some time to elapse.

Does pianoscope use FFT analysis to determine pitch? If so, what FFT size or sizes are used? Is the freeze duration actually changing the FFT size, giving better or worse frequency resolution as a result?

Frank Illenberger

David Kissam You can configure both the length of the freeze window and the delay after the attack under Main Menu > Settings > Indicator > Freeze

There is a section in the user manual about it.

By default, the delay setting is zero for all notes, which means that pianoscope starts recording for the freeze directly after the attack. The default recording duration depends on the note. It is 300ms for the midrange, 400ms for the low bass and 800ms for the treble.

I don't disclose the frequency estimation algorithms, but you are correct that the achieved frequency resolution is dependent on the length of the freeze window, but in a more subtle way: Even with only 300ms, the absolute frequency resolution for a single isolated partial frequency is high enough for piano tuning purposes. But if you have two or more closely spaced frequencies–like with strings with false beats– the freeze window length makes a difference in how good pianoscope can separate the individual frequencies. I have made a short video about false beats which touches this topic.
The default settings in pianoscope are therefore a tradeoff between fair false-beat resolution and working speed, because with a higher setting the user has to wait longer after an attack which slows down the tuning work.

Pianoscope offers three default sets of durations. You can easily switch between them in the tuning screen by long-pressing the snowflake symbol in the main toolbar. The "Long" set records for 2 seconds by default. It can make sense to temporarily switch to a set with longer durations if you encounter notes with bad false-beats and pianoscope is giving you an inconsistent pitch display. But this may also have other reasons as shown in the video.

You can customize the durations in all sets and go as high as five seconds if desired.

David Kissam

Frank Illenberger Thanks for the reply. I had read that part of the manual, but your explanation here makes it clearer to me. I had forgotten about the option to set delay and duration separately, which, now that I think about it, mostly answers my question.

So, is it correct to say that everything that happens with the pitch within the freeze window (or "duration" as it is called in the app) affects the final value that is displayed? For example, if the pitch starts high and falls smoothly throughout the length of the freeze duration, I should expect the value displayed to be somewhere between the starting (highest) and ending (lowest) pitches. Is that right?

And, if that's the case, then setting a longer freeze duration for better handling of false beats would also mean that the later part of the note has more influence on the final displayed pitch, since pianoscope is listening longer after each attack. Or is that not the case?

Frank Illenberger

David Kissam Yes, both are correct.