Integral of a signal using delay buffer: how to get the last X samples from a delay~ buffer?
Julia Merino
Apr 13 2023 | 12:27 pm
Hi, I am implementing a patch to calculate the loudness of an incoming signal for an interactive live performance system. This system will have a parameter to change the duration of the sliding window between 1 and 30 seconds. My first approach was to use average~ however this doesn't work when suddenly changing the time interval from 1s to 10s for instance as I guess the buffer doesn't have access to the samples of the last 10s. For this reason, I've thought of implementing the average calculation by always storing in a delay buffer the last 30 seconds and from there get the last T time samples to calculate the accumulation (integral) and then divide that between T-time samples to get the average.
My question is how to get the last X samples from a delay~ buffer?
Thanks a lot for you help!
- Source AudioApr 13 2023 | 2:39 pmrecord 30 seconds of audio into buffer and read whatever portion of it using peek . As alternative, you could store average per period, like 10 - 100 ms instead of each sample which would make storage and calculations much more effective
- Julia MerinoApr 13 2023 | 3:13 pmThat's a good shout. However, how could I constantly update the buffer with the new incoming samples?
- Source AudioApr 14 2023 | 7:49 amhere is what I woud do : get average level of 1 second which is your minimum report length by taking 100 readings and averaging them. meter~ set to report 10ms interval -> zl.group 100 = 1000 ms 30 average values get inserted into coll , you set how many last seconds get taken into calculation of average level.Max Patcher
In Max, select New From Clipboard. - Julia MerinoApr 14 2023 | 2:58 pmThank you very much! I ended up using a slightly different approach using zl.stream instead but all seems to be working fine!
- Roman ThileniusApr 14 2023 | 3:55 pmif you need to access samples other than the last one, why not use a tapping buffer instead of delay~ ?i build loudness metering also around average~ because it is actually cheaper than using individual math objects. no idea why you would like to modulate the window size though. for loudness the mean-sqare is normally measured in chunks of 400 ms with 75% overlap. which is roughly what you get when using average~ with 400, followed by rampsmooth~ with 400, and then snapshot~ the values to be displayed (or accumulated).alternatively to the rampsmooth+ you could take the analysed 100ms values and interpolate those values over 5 values. (2 in both directions. nowadays done using zl.stream, exactly.)
- Julia MerinoApr 14 2023 | 6:29 pmThanks Roman! I actually checked your loudness meter :) My client wants to be able to adjust the sliding window. I went for taking the avg~ in chunks of 100ms and making a 300-long list (30 seconds) with zl.stream so I could always have access to the last N average samples if the sliding window was increased.
