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| strokeanalysis:stroke_analysis [2013/02/03 19:48] – deva | strokeanalysis:stroke_analysis [2013/02/21 12:35] (current) – deva | ||
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| The experiment was performed on an Axis Longboard pedal only, but should for good measure be performed on other types of pedals too sometime in the future... | The experiment was performed on an Axis Longboard pedal only, but should for good measure be performed on other types of pedals too sometime in the future... | ||
| - | A movie was recorded with 200fps | + | A movie was recorded with 220fps |
| {{: | {{: | ||
| {{: | {{: | ||
| Line 17: | Line 17: | ||
| Note the white dots on the center-of-axis as well on the mallet. These were added in order to be able to identify the exact mallet and origo positions in each image. | Note the white dots on the center-of-axis as well on the mallet. These were added in order to be able to identify the exact mallet and origo positions in each image. | ||
| + | ====Meaurements==== | ||
| + | ===Single stroke=== | ||
| + | ^ Position ^ Vector | ||
| + | | 0 | (-255,391) | 466.80 | 0.00 | 0.00 | 0.00 | | ||
| + | | 1 | (-247,394) | 465.02 | 1.03 | 1.03 | 226.07 | | ||
| + | | 2 | (-235,405) | 468.24 | 2.99 | 1.96 | 431.07 | | ||
| + | | 3 | (-210,420) | 469.57 | 6.55 | 3.56 | 783.04 | | ||
| + | | 4 | (-176,440) | 473.89 | 11.31 | 4.76 | 1048.00 | | ||
| + | | 5 | (-134,458) | 477.20 | 16.80 | 5.49 | 1208.50 | | ||
| + | | 6 | (-74,480) | 485.67 | 24.35 | 7.54 | 1659.71 | | ||
| + | | 7 | (-6,491) | 491.04 | 32.41 | 8.06 | 1774.08 | | ||
| + | | 8 | (73,493) | 498.38 | 41.53 | 9.12 | 2007.03 | | ||
| + | | 9 | (146,480) | 501.71 | 50.03 | 8.50 | 1868.96 | | ||
| + | | 10 | (232,451) | 507.17 | 60.33 | 10.30 | 2266.84 | | ||
| + | | 11 | (240,446) | 506.47 | 61.40 | 1.06 | 233.99 | | ||
| + | | 12 | (229,452) | 506.70 | 59.98 | -1.42 | -311.73 | | ||
| + | A plot of the angle velocities reveal a rather ' | ||
| + | {{: | ||
| - | ====Single stroke==== | + | ===Stroke sequence=== |
| ^ Position ^ Vector | ^ Position ^ Vector | ||
| | 0 | (-255,391) | 466.80 | 0.000000 | | 0 | (-255,391) | 466.80 | 0.000000 | ||
| Line 33: | Line 51: | ||
| | 11 | ( 240,446) | 506.47 | 61.396774 | 1.063580 | | 11 | ( 240,446) | 506.47 | 61.396774 | 1.063580 | ||
| | 12 | ( 229,452) | 506.70 | 59.979810 | -1.416964 | | 12 | ( 229,452) | 506.70 | 59.979810 | -1.416964 | ||
| - | |||
| - | A plot of the angle velocities reveal a rather ' | ||
| - | {{: | ||
| - | |||
| - | ====Stroke sequence==== | ||
| - | ^ Position ^ Vector | ||
| - | | 0 | (-381,215) | 437.48 | 0.000000 | ||
| - | | 1 | (-370,236) | 438.86 | 3.095041 | ||
| - | | 2 | (-356,267) | 445.00 | 7.433667 | ||
| - | | 3 | (-331,304) | 449.42 | 13.129037 | 5.695370 | ||
| - | | 4 | (-298,346) | 456.64 | 19.826380 | 6.697343 | ||
| - | | 5 | (-255,389) | 465.13 | 27.317846 | 7.491466 | ||
| - | | 6 | (-203,425) | 470.99 | 35.032433 | 7.714587 | ||
| - | | 7 | (-144,458) | 480.10 | 43.110075 | 8.077642 | ||
| - | | 8 | ( -78,483) | 489.26 | 51.390233 | 8.280159 | ||
| - | | 9 | ( -14,494) | 494.20 | 58.940436 | 7.550203 | ||
| - | | 10 | ( 54,496) | 498.93 | 66.777144 | 7.836708 | ||
| - | | 11 | ( 110,492) | 504.15 | 73.166538 | 6.389394 | ||
| - | | 12 | ( 162,483) | 509.44 | 79.105414 | 5.938875 | ||
| - | | 13 | ( 198,468) | 508.16 | 83.495869 | 4.390456 | ||
| - | | 14 | ( 216,464) | 511.81 | 85.526559 | 2.030689 | ||
| - | | 15 | ( 210,467) | 512.04 | 84.776208 | -0.750351 | ||
| The graph of these angle velocities show a picture rather more ' | The graph of these angle velocities show a picture rather more ' | ||
| {{: | {{: | ||
| Line 60: | Line 56: | ||
| ====Evaluation===== | ====Evaluation===== | ||
| ===Samplerate=== | ===Samplerate=== | ||
| - | The maximum angle velocity was found in the single stroke and was 2061 degrees per second. | + | The maximum angle velocity was found in the single stroke and was 2266.84 |
| That the maximum angle velocity should be found in the stroke type is not surprising since a single stroke is the result of the hardest foot impact on the pedal.\\ | That the maximum angle velocity should be found in the stroke type is not surprising since a single stroke is the result of the hardest foot impact on the pedal.\\ | ||
| If we assume the target latency to be at most 1ms and we assume that the software is responding in the area of microseconds and therefore negligible we can estimate the target ADC sampling resolution.\\ | If we assume the target latency to be at most 1ms and we assume that the software is responding in the area of microseconds and therefore negligible we can estimate the target ADC sampling resolution.\\ | ||
| - | Lets start by pointing out that since the video framerate was 200fps | + | Lets start by pointing out that since the video framerate was 220fps |
| - | The single stroke took 11 frames in total which is 55ms and during this time the mallet moved 61.4 degrees, resulting in a minimum resolution of 1.12 samplings per millisecond. | + | The single stroke took 11 frames in total which is 50ms and during this time the mallet moved 61.4 degrees, resulting in a minimum resolution of 1.23 samplings per millisecond. |
| - | However, if we look at the diff in the last two velocities before the impact it was 10.3 degrees in 5ms it is evident that the minimum resolution should be higher, namely 2.06 samplings per millisecond. | + | However, if we look at the diff in the last two velocities before the impact it was 10.3 degrees in 4.55ms |
| - | Ergo: **A sampling of 2kHz should be sufficient.** | + | Ergo: **A sampling of approximately |
| - | //However// ... the result of this mechanism is the playing of a sample at probably 44.1kHz or 48kHz and in order to avoid phasing problems when mixing with the analogue | + | //However// ... the result of this mechanism is the playing of a sample at probably 44.1kHz or 48kHz and in order to avoid phasing problems when mixing with the analogue |
| ===Bit precision=== | ===Bit precision=== | ||
| - | When considering bit precision it is the lowest angle velocity upon impact that ar ethe worst case scenario. | + | When considering bit precision it is the lowest angle velocity upon impact that are the worst case scenario. |
| - | If we therefore look at the stroke sequence we can observe a 2.03 degrees between the last two frames, giving 0.406 degrees in the last millisecond. | + | If we therefore look at the stroke sequence we can observe a 2.03 degrees between the last two frames, giving 0.446 degrees in the last millisecond. |
| - | If we divide the entire 84 degree interval into 0.406 degree segments the result is a minimum of 207 steps. | + | If we divide the entire 84 degree interval into 0.446 degree segments the result is a minimum of 188 steps. |
| Ergo: **A bit precision of 8 should be sufficient.** | Ergo: **A bit precision of 8 should be sufficient.** | ||
| Line 89: | Line 85: | ||
| If say the drummer hits twice as hard (double the angle velocity) and cannot accept latency at more than 0.5ms the calculations from above will be:\\ | If say the drummer hits twice as hard (double the angle velocity) and cannot accept latency at more than 0.5ms the calculations from above will be:\\ | ||
| - | Samplerate: 2.06 * 2 degrees in 5ms = **8kHz sampling** (but still it should be considered to use 44.1kHz or 48kHz to avoid phasing problems)\\ | + | Samplerate: 2 * 2.03 degrees in 4.55ms |
| A very slow stroke is the worst case scenario when considering the bit precision since we need more steps in the final steps of the swing. | A very slow stroke is the worst case scenario when considering the bit precision since we need more steps in the final steps of the swing. | ||
| If say the angle velocity is half of the measured one and the drummer is sensitive to latencies above 0.5ms the number of needed steps will go up by factor of 4: | If say the angle velocity is half of the measured one and the drummer is sensitive to latencies above 0.5ms the number of needed steps will go up by factor of 4: | ||
| - | Bit precision: | + | Bit precision: |
