Panning different sound sources

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bg_ie@yahoo.com - 19 Aug 2006 15:38 GMT

Hi all,

I have two fm instruments with slightly different modulation indices. I
have both instruments playing the same notes at the same time with the
same asdr. I have one of the fm instruments hard panned to the left and
the other to the right. In other words, each instrument has its own
speaker. What I'd like to do is fade out the first instrument and fade
in the second instrument such that the volume level remains constant,
but that you get the illusion of panning and a gradual change of
timbre.

So my question is, how should the fade work, should it be linear or
logarithmic or something else?

Thanks for your help,

Barry.

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Jens Rodrigo - 19 Aug 2006 16:26 GMT

> I have two fm instruments with slightly different modulation indices.
> I
[quoted text clipped - 8 lines]
> So my question is, how should the fade work, should it be linear or
> logarithmic or something else?

Use the sinus/cosinus law. Fade the loud instrument with a
cosinus amplitude curve down and the other instrument with the
sinus amplitude up. Then the sum of the power of both instruments
stays constant. When cos and sin meet, the level is 3 dB down.

Cheers Jens

Reply to this Message

Jens Rodrigo - 19 Aug 2006 16:36 GMT

>> I have two fm instruments with slightly different modulation indices.
>> I
[quoted text clipped - 17 lines]
>
> Cheers Jens

And so looks your fading law which is also the panpot law:
http://www.mu-s.com/images/M-images/edu/panpot.gif
You see, its neither linear nor logarithmic.

Cheers Jens

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bg_ie@yahoo.com - 24 Aug 2006 10:14 GMT

> >> I have two fm instruments with slightly different modulation indices.
> >> I
[quoted text clipped - 23 lines]
>
> Cheers Jens

Thanks for the reply, another quick question though. Is the cosine/sine
fade with respect to a linear scale or a dB scale. For example, is the
following equation valid -

do
{
d+=1/frequency;

fade = cos(PI/_length*(d-_startTime)/2)
*(_startVolume - _finishVolume )+_finishVolume;

signal*=fade;
}
while(d<(_length+_startTime));

where _startVolume and _finishVolume are linear values such as 300 and
30000, with these values in the range -32768 to +32767 for 16 bit
audio?

Thanks for your help,

Barry.

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Jens Rodrigo - 24 Aug 2006 10:45 GMT

bg_ie@yahoo.com> schrieb:

> Thanks for the reply, another quick question though. Is the
> cosine/sine
[quoted text clipped - 15 lines]
> 30000, with these values in the range -32768 to +32767 for 16 bit
> audio?

The sinus and cosinus curves go with the amplitude
values of the voltage.
Here you find the sinus/cosinus as dB curves:
http://www.sengpielaudio.com/Panoramaregler-Panpot.pdf#search=%22panpot%22

Cheers Jens

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Natural Science Forum / Physics / Acoustics / August 2006

Panning different sound sources