Timeline for Double the "speed", double the frequency?
Current License: CC BY-SA 3.0
23 events
| when toggle format | what | by | license | comment | |
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| Nov 27, 2016 at 13:27 | comment | added | Dan Boschen | @A_A Terrific! Thanks for this very interesting post! | |
| Nov 27, 2016 at 13:24 | comment | added | A_A | @DanBoschen, it doesn't really matter within reason. See answers to this post. Thank you for the dsp-puzzle tag :) | |
| Nov 27, 2016 at 13:20 | vote | accept | A_A | ||
| Nov 27, 2016 at 13:20 | answer | added | A_A | timeline score: 2 | |
| Nov 25, 2016 at 21:51 | comment | added | Dan Boschen | @A_A Is the speedup you describe done by playing the samples faster while not changing the sample rate (meaning skipping samples as in my example such as to cause aliasing)? | |
| Nov 25, 2016 at 16:20 | answer | added | Hilmar | timeline score: 3 | |
| Nov 24, 2016 at 22:01 | comment | added | A_A | @nispio As with previous comments that are more of a statement, I don't know what to respond so I am going to go with "Yes, that is a correct observation". And yes, this does play a role in this phenomenon. Dan, this could be the basis or the start towards an answer, similarly to nispio's comment. Finally, many thanks to whoever responded so quickly to the last message about converting user Dan Boschen's response to a message. | |
| Nov 24, 2016 at 21:53 | comment | added | Dan Boschen | What could cause this phenomena to occur is if the "speeding up" process was done by decimating: to play back twice as fast, while not changing the sample rate, we would skip every other sample. As long as the signal frequency was less than 1/4 the sampling rate, the signal frequency would double as expected. However, if the signal frequency was greater than 1/4 the sampling rate, alias frequencies would occur in the resulting Nyquist spectrum. For example, a signal at 0.3 fs would double to 0.6 fs after a decimate by 2, which would alias to 0.4 fs. | |
| Nov 23, 2016 at 17:31 | comment | added | nispio | Harmonic content that was outside the limits of human hearing before can become part of the perceived pitch after the frequency doubling. | |
| Nov 21, 2016 at 11:33 | comment | added | A_A | @msm No worries. Faced with a puzzle, I have had similar behaviour in the past :) I think that your thinking process is drawing you near part (or maybe even the whole) of the answer. | |
| Nov 21, 2016 at 10:33 | comment | added | msm | @A_A Oh, sorry I didn't get your message. Honestly, I am not so good in puzzles but I don't think if you pitch-shift a white noise it sounds much different. Also, a chirp signal seems to be a similar case. | |
| Nov 21, 2016 at 9:47 | history | edited | A_A | CC BY-SA 3.0 |
Provided further clarification given comments and attempts at answers
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| Nov 21, 2016 at 1:40 | history | tweeted | twitter.com/StackSignals/status/800514296069361668 | ||
| Nov 21, 2016 at 0:07 | comment | added | ederwander | imagine that do you have a signal at 5000 Hz sampled at 44100 Hz, all OK 5000 Hz is inside the nyquist boundarie, now imagine resample this signal to 8000 Hz where go this frequency if we are out of the nyquist ? maybe are you talking about cases like this. | |
| Nov 20, 2016 at 17:45 | history | edited | A_A | CC BY-SA 3.0 |
Made a hint provided at the comments, more concrete.
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| Nov 20, 2016 at 9:40 | comment | added | percusse | can also be the case of aliasing if the samples are skipped to match the playback speed | |
| Nov 20, 2016 at 8:59 | history | edited | A_A | CC BY-SA 3.0 |
Given the comments, I decided to modify some words to hint better at what "double the speed" means.
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| Nov 20, 2016 at 8:57 | comment | added | A_A | @robertbristow-johnson I don't know what to respond, that is correct. So, if it has to be framed under a pitch shifting framework: Are there any waveforms that if you pitch shifted them by 2 they would still sound very very very similar? MSM: Giving away the waveform is like giving away the puzzle and this is a "dsp-puzzle". Also, "twice the recording speed" or "twice as fast" is already defined in the post (?). | |
| Nov 19, 2016 at 23:54 | comment | added | msm | It would be more clear if you add some instances of the sample cases you pointed out, as well as the way you playback with twice recording speed. | |
| Nov 19, 2016 at 23:21 | comment | added | robert bristow-johnson | actually, what you are describing is just the "time scaling" operation. | |
| Nov 19, 2016 at 23:20 | history | edited | robert bristow-johnson | CC BY-SA 3.0 |
added 3 characters in body
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| Nov 19, 2016 at 23:19 | comment | added | robert bristow-johnson | what you are describing is called "pitch shifting" and it can be considered the combination of two operations: "time scaling" and "sample interpolation" (or "sample rate conversion" even though we are not changing the sample rate). the latter operation is mathematically well-defined. it speeds up and raises the pitch together. the time scaling operation is less well defined. it makes a sound longer (or shorter) without changing the pitch. so, to up-pitch a sound, first you have to time-scale it to be longer (and the same pitch), then apply SRC to shorten it to the original. | |
| Nov 19, 2016 at 23:02 | history | asked | A_A | CC BY-SA 3.0 |