[Sidefx-houdini-list] spectrum node questions

Edward Lam edward at sidefx.com
Sun Mar 1 19:30:39 EST 2015


On Sun, March 1, 2015 13:07, Sam Cuttriss wrote:
> i mostly crash.

If you have a scene that can reproduce the crash, you should submit it.
Although if you're dealing with lots of audio data, this can also be due
to running out of memory because CHOPs will decompress all the audio into
raw form with 8 bytes per sample. So at 44.1KHz, we're talking about ~344
KB per second for 1 channel, double this if we're talking about stereo.
Then for each CHOP that you append, the data will be copied unless you
have the Unload parameter set on the input.

>>    - the waveform does not look like it is correctly informed by the
>>    frequency magnitude curve.

The documentation here is a bit bad. From
http://www.derivative.ca/wiki088/index.php?title=Spectrum_CHOP, it
mentions:
"""
When converting a signal to its spectrum, two channels are created from
the one containing the signal. One channel contains the magnitude of the
frequency components, and the other contains the phase. The channels are
named <channel name><suffix>, where <suffix> is the magnitude or phase
suffix.
To determine the frequency that a given sample represents, use the formula:
Freq = 2 x (sample#) x (Sample Rate) / (Channel Length)
Where 'Sample Rate' and 'Channel Length' both refer to the Spectrum CHOP's
rate and length.
"""
Are you running into this?

>>    - even though im telling the waveform to start at sample 0 its
>>    starting at frame 1 so im not certain its sampling the correct data.

Houdini's "frame" units starts at 1 frame for 0 seconds in the scene due
to legacy reasons. The "sample" unit is more sensible in that it also
starts at 0 for 0 seconds in the scene.

>>    - i need the spectrum node to continue sampling the first frame worth
>>    of samples and outputting a waveform rather than stopping after the
first.

Not sure what you mean here.

>> am i allowed to attach hiplc files to the list?

There are no attachments allowed to the list. Have you tried asking on the
sidefx.com or odforce.net forums?

Best Regards,
-Edward




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