say when you have an idea for a melody, and you know the time signature you set the quantization.
you select a record trigger, this record trigger reacts as soon as you begin inputting notes it would calculate the bpm based on your input + lines per beat divided by quantization.
so the interval between note 1 and and the placement of note 2 using quantization will be the bpm. this being based on your quantization & lpb
i dearly wish some program had this, but mainly renoise. 
note i did not write, tap tempo in the heading.
cuz tap tempo does not describe the function of what i’m getting at.
tap tempo is pressing a button until the bpm is near or at the tempo you need.
this idea is using the timing between quantized notes to calculate the bpm.
it could be called like tap tempo 2.0, because it is not tap tempo.
i don’t want tap tempo at all. cuz it’s too much like reverse engineering.
i want BPM LEARNING, cuz it is Direct Engineering.
you can change the heading to Bpm Learning (Tap Tempo 2.0)
cuz in this way the tap tempo would be intrinsic to the actual melody! 
it’s like this:
you set renoise up to begin recording with the correct quantization and lpb.
you play the melody on the keyboard. (renoise in the background calculating the bpm, so it can place the notes in the correct place)
then by the time you finish the melody. you have the correct bpm.
and all notes in the correct spot.
tap tempo 2.0
BPM learning!
to explain this further, tap tempo implies 2 processes.
tap tempo being the process to get to the correct bpm.
BPM Learning being the process of incorporating tap tempo in an intuitive manner by merging this into 1 process of inputting the melody/timing directly.
Doesn’t Ableton do something like this? I seem to remember hearing it can detect the tempo you’re playing at or something
i will go browse the abelton features.
looks like they have to do it manually.
i just realized how complicated this actually is.
can’t base it on the timing between note 1 and note 2.
because based on quantization the only place for the next note is the next slot in quantization.
so would need to base it on the timing between all the notes, and the pattern length + quantization + LPB.
to equal the BPM.
so it would be more like pattern length and LPB divided by quantized notes to equal BPM.
my math may be off, but this is much closer to the actual formula of what i’m getting at.
okay now i see the main thing of what makes this difficult and tough to figure out. is how to tell it when to stop. since the stop point is most important to getting the notes in the correct placement.
hmm, play the sequence Twice. since renoise is pattern based. playing the notes twice could give an algorythm a discernable sequence.
giving it a basis to work with and compare.
any sort of tap tempo would be awesome.
maybe make it reverse engineer a tempo from loop points in the sample editor; the ability to name how many beats long a loop is and then hit a button to make that one happen. Diluting the idea some, but maybe this would be easier to implement? I do like the sound of your idea anyhow…
well i admit i was cheating when i came up with the last solution.
when i wrote play the sequence twice. this really isnt a solution since the length of the sequence couldn’t neccesarily be determined in this fashion.
something else would need to be happening. what exactly i’m not sure.
in order for it to be open ended, and to expand on in the future. the whole process would need to be analyzing the input process in realtime along with placing the input in realtime like a rubber band being stretched onto a group of wheels whose axles are already grouped with rubber bands. (wheels being notes, axles being location)
rubberband being the pattern.