SoundBlaster sampling frequency accuracy

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3 total messages Started by Peter Sj{gren Thu, 20 Aug 1992 08:49

#471

Author: Peter Sj{gren
Date: Thu, 20 Aug 1992 08:49

21 lines
1147 bytes

Hi,

I have an old version (1.5) of the SoundBlaster soundcard from Creative Labs
for PC and I would like to do accurate frequency measurements. As a first 
experiment I tried to record a 440 Hz tuning fork at 11025 Hz sampling 
frequency, but I got a frequency of about 436 Hz (give or take 0.7 Hz).

I therefore wonder about the accuracy of the sampling frequency and other
data on this model (1.5) and if they are better on later versions.


By the way: does anyone know the email-address to Creative Labs?

Thank you for your answers!

Peter Sjogren
Stockholm
Sweden


please answer to pesjogre@nada.kth.se or peter@jada.se

Re: SoundBlaster sampling frequency accuracy

#559

Author: Gilles Gravier
Date: Fri, 21 Aug 1992 08:45

28 lines
1475 bytes

In article <1992Aug20.084909.5385@kth.se> pesjogre@nada.kth.se (Peter Sj{gren) writes:
>Hi,
>
(... DELETED ...)
>
>I therefore wonder about the accuracy of the sampling frequency and other
>data on this model (1.5) and if they are better on later versions.
>

	Ah, I suggest you read the programmers manual of the Sound Blaster...
I don't have it at work with me, but you'll notice that the sampling
frequency is stored in a specific format... Just count the bits, and you'll
get the acuracy with which the sampling frequency is defined... That should
help you...

	As an example, say you're using 8 bits to define a frequency... And
Your Frequence can go from 0 to 22000 Hz... Then you have a 86 Hz acuracy.
At 11000 KHz, it's 43 Hz...  And so on... 440 Hz give 2 Hz accuracy.

	Does this help?

Gilles.

-- 
 This message has been brought to you by Gilles GRAVIER - corwin@ensta.fr
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       sure, you realize,  that what you heard is not what I meant.

Re: SoundBlaster sampling frequency accuracy

#575

Author: Gilles Gravier
Date: Sat, 22 Aug 1992 20:47

32 lines
1934 bytes

In article <1992Aug21.113836.20589@email.tuwien.ac.at> martin@eichow.tuwien.ac.at writes:
>
>So the problem is not one of using 8 bits, as in your example, to represent
>the 440 Hz out of 22 kHz one might want to record, which would give a 86 Hz
>inaccuracy and render the sound card unusable. Rather, it is one of getting
>the input and output sampling frequencies to be the same.


	I must have explained myself badly (sorry, I'm French... My English is
not as it could be). What I was saying is that in a .VOC file, the sampling
frequency is coded on one byte, at offset 4 in a Voice Data block. The
sampling rate is the determined by using the formula:

SR(1 byte)=256-1000000/SamplingRate

	Which means exactly what I was saying... As the sampling rate is
defined on 1 byte, it's precision is of 1/256=0.4% which means that when
sampling ANYTHING at 11000Hz, you may actually be sampling at anything
between 10989 and 11111 Hz... and, when replaying, you have the same
possible variations... Dont be surprised if the sound you sample then play
again varies... You may have sampled at 10989 and played at 11111 Hz...
Or vice versa...

	A Sound Blaster never was precise...

Gilles.

-- 
 This message has been brought to you by Gilles GRAVIER - corwin@ensta.fr
                       ***** Amber Forever! *****
    I know you believe you understand what you think I said, but I am
       sure, you realize,  that what you heard is not what I meant.

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