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Author Topic: Odd sound: Sine/Triangle low frequency  (Read 7478 times)

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usrfriendly

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Odd sound: Sine/Triangle low frequency
« on: July 11, 2008, 05:17:11 »

Since I started using Nitrotracker (0.3), i've noticed that if I play a sine or triangle wave at a low frequency, it gives the low tone, and a bit of a high-pitched, quiet tone on top of it.  I tested the same .xm file on my DS and on MilkyTracker (PC), and the high pitched tone wasn't there.  Is there some sort of explanation for this (my guess is the software, LSDJ does the same thing in an emulator on my DS)
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0xtob

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Re: Odd sound: Sine/Triangle low frequency
« Reply #1 on: July 11, 2008, 12:17:21 »

I haven't observed this myself, but my guess would be that the DS's sound hardware is to blame. Probably the AD converter doesn't interpolate the values given to it, so a sample played back at very low sampling rate will have "steps" (imagine this like zooming into an image into an image editor until you see the pixels), which cause high pitched noise.

This could be fixed by doing the sound rendering in software, but then we wouldn't have original DS sound any more :)
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m0d

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Re: Odd sound: Sine/Triangle low frequency
« Reply #2 on: July 11, 2008, 12:31:56 »

Hmmm: Aliasing, is this the correct term?
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raina

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Re: Odd sound: Sine/Triangle low frequency
« Reply #3 on: July 11, 2008, 13:36:42 »

In MilkyTracker, try setting Config > I/O > Resampling to No interpolation. Sound familiar?

0xtob

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Re: Odd sound: Sine/Triangle low frequency
« Reply #4 on: July 11, 2008, 16:17:19 »

m0d: Aliasing is the effect that occurs when you sample a signal of some frequency at a sampling frequency that is less than twice the frequency you're sampling. Then you won't be able to capture the frequency of the tone you want to record, but you'll get an unwanted "alias" frequency.

The effect of playing back a sample at a very low frequency is that a spurious frequency is generated by the "steps" of the "stairs" that are the samples of your sound stretched to multiple samples in the output signal.

Aliasing might occur in NitroTracker when you play back a sample at a too high frequency, because the DS's hardware mixer downsamples everything to 32khz. So you have to use multiple samples per instrument to avoid this.
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raina

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Re: Odd sound: Sine/Triangle low frequency
« Reply #5 on: July 11, 2008, 16:55:31 »

Hooray for .XI :)

usrfriendly

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Re: Odd sound: Sine/Triangle low frequency
« Reply #6 on: July 12, 2008, 00:39:59 »

In MilkyTracker, try setting Config > I/O > Resampling to No interpolation. Sound familiar?

yeah, that's what happened.  i've also run into high-frequency aliasing, as 0xtob mentioned.  i'm not sure how to combine samples for an instrument, though, in any tracker, is there somewhere i can go to find out?
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0xtob

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Re: Odd sound: Sine/Triangle low frequency
« Reply #7 on: July 12, 2008, 11:28:31 »

Sure, there's a tutorial on it in the documentation:
http://nitrotracker.tobw.net/index.php?cat_id=4#instruments
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bithog

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Re: Odd sound: Sine/Triangle low frequency
« Reply #8 on: July 12, 2008, 18:07:00 »

i kind of like that sound. I'm using a sine pitched way down in  track now. its real durty. Aint that the beauty of this thing? To get off the audiophile Lavry A/D D/A converter, 24bit 192khz anal trip and jam with this baby?

well for me it is anyway.
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raina

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Re: Odd sound: Sine/Triangle low frequency
« Reply #9 on: July 12, 2008, 21:39:59 »

The sound can often work as an effect adding a little colour to the mix. Generating sine and triangle tones at very low volume and frequency and boosting them afterwards produces nice jagged waves. :)
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