Looking for digital filters of A, B, C weighting

[DigitalSignal]

Hi there,

We are looking for the guidance of the digital implementation of A, B
and C weighting in the sound level meters. Can anybody provide one or
pointing to the right direction? Thanks a lot.

www.go-ci.com
Handheld Data Recorder/Dynamic Signal Analyzer

[Joe Kotroczo]

On 20/12/07 23:54, in article
,
"DigitalSignal" > wrote:

> Hi there,
>
> We are looking for the guidance of the digital implementation of A, B
> and C weighting in the sound level meters. Can anybody provide one or
> pointing to the right direction? Thanks a lot.

What do you want to know that you can't find in IEC179 ?

--
Joe Kotroczo

[Don Pearce]

On Thu, 20 Dec 2007 14:54:49 -0800 (PST), DigitalSignal
> wrote:

>Hi there,
>
>We are looking for the guidance of the digital implementation of A, B
>and C weighting in the sound level meters. Can anybody provide one or
>pointing to the right direction? Thanks a lot.
>
The equations for the functions are all here

http://en.wikipedia.org/wiki/A-weighting

d

--
Pearce Consulting
http://www.pearce.uk.com

[DigitalSignal]

On Dec 20, 3:29 pm, (Don Pearce) wrote:
> On Thu, 20 Dec 2007 14:54:49 -0800 (PST), DigitalSignal
>
> > wrote:
> >Hi there,
>
> >We are looking for the guidance of the digital implementation of A, B
> >and C weighting in the sound level meters. Can anybody provide one or
> >pointing to the right direction? Thanks a lot.
>
> The equations for the functions are all here
>
> http://en.wikipedia.org/wiki/A-weighting
>
> d
>
> --
> Pearce Consultinghttp://www.pearce.uk.com

Don, Joe, Thanks a lot.

James Zhuge

[Scott Dorsey]

DigitalSignal > wrote:
>
>We are looking for the guidance of the digital implementation of A, B
>and C weighting in the sound level meters. Can anybody provide one or
>pointing to the right direction? Thanks a lot.

The numbers are in the B&K "Architectural Acoustics" book. Plug them
into the general filter function in Matlab. Voila.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Joe Kotroczo]

On 21/12/07 0:29, in article , "Don Pearce"
> wrote:

>> We are looking for the guidance of the digital implementation of A, B
>> and C weighting in the sound level meters. Can anybody provide one or
>> pointing to the right direction? Thanks a lot.
>>
> The equations for the functions are all here
>
> http://en.wikipedia.org/wiki/A-weighting

If they want to produce a meter that is to be sold commercially (which I
assume since they appear to be in that business) they would IMHO be better
of to get the standards document from the IEC than to trust in Wikipedia.

Also, there seems to be more to it than just the weighting curves, the
preview of that documents (which one can download free of charge) mentions
stuff like: "Directional response, Level linearity, Self-generated noise,
Time weightings F and S, Toneburst response, Response to repeated
tonebursts", etc.

And to correct myself, the document is apparently now called IEC 61672. Can
be had for 179 CHF (Swiss Francs), which is 108 Euros at current exchange
rates. Quite a bit of money for 85 pages, but cheaper than a lawyer.




P.S.

Since the meter that's advertised on the OPs website seems to be a pretty
fancy one, it might be worth it to encourage them to include _all_ the
curves/standards. One never knows when they might be useful.

There's ISO 226:2003, which is only 18 pages, (probably only the curves, and
the rest in other documents), for 90 CHF. This is a new and revised set of
curves, which I think that this is likely to supersede the curves mentioned
above, which date from 1961. More on that here:
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles&VIEW=full&id=1
7

And there's yet another curve, the ITU-R 468 curve, which is "is widely used
when measuring noise in audio systems", except for the US apparently.
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles&VIEW=full&id=1
0

And to be complete, there's also "Acoustics -- Method for calculating
loudness level" : ISO 532:1975. (aka DIN 45631)
I am told that this method gives you a measurement in "sone", see:
http://en.wikipedia.org/wiki/Sone and
http://www.aes.org/e-lib/browse.cfm?elib=1376

(The "sone" unit is actually being used, a German computer magazine started
using it some years ago, after their readers had started complaining that
stuff that had equal dB(A) levels in the mags tests didn't sound equally
loud to them. Nearly all German computer mags have adopted it since.)


--
Joe Kotroczo

[Eeyore]

Don Pearce wrote:

> DigitalSignal wrote:
> >
> >We are looking for the guidance of the digital implementation of A, B
> >and C weighting in the sound level meters. Can anybody provide one or
> >pointing to the right direction? Thanks a lot.
>
> The equations for the functions are all here
>
> http://en.wikipedia.org/wiki/A-weighting

How easy is it to convert that into DSP code ?

Graham

[DigitalSignal]

Joe, thank you for your excellent description and guidance.

We recently released a handheld dynamic signal analyzer (www.go-
ci.com) with excellent dynamic range. Hopefully it can be converted
into a sound level meter. But I wonder if sound level meter needs 8
channels. It seems most of them just have one channel.

James Zhuge
www.go-ci.com

[Don Pearce]

On Fri, 21 Dec 2007 03:08:57 +0000, Eeyore
> wrote:

>
>
>Don Pearce wrote:
>
>> DigitalSignal wrote:
>> >
>> >We are looking for the guidance of the digital implementation of A, B
>> >and C weighting in the sound level meters. Can anybody provide one or
>> >pointing to the right direction? Thanks a lot.
>>
>> The equations for the functions are all here
>>
>> http://en.wikipedia.org/wiki/A-weighting
>
>How easy is it to convert that into DSP code ?
>
>Graham

As easy as any transfer function, I would have thought. I've never
actually designed a filter from that starting point, though.

As the Irishman said "No, you can't get there from here. You need to
start from over there."

d

--
Pearce Consulting
http://www.pearce.uk.com

[Arny Krueger]

"Eeyore" > wrote in
message
> Don Pearce wrote:
>
>> DigitalSignal wrote:
>>>
>>> We are looking for the guidance of the digital
>>> implementation of A, B and C weighting in the sound
>>> level meters. Can anybody provide one or pointing to
>>> the right direction? Thanks a lot.
>>
>> The equations for the functions are all here
>>
>> http://en.wikipedia.org/wiki/A-weighting
>
> How easy is it to convert that into DSP code ?

I understand that the usual approach involves Matlab.

The usenet comp.dsp seems to be alive and well, if you catch my drift.

[Mark]

On Dec 21, 8:31*am, "Arny Krueger" > wrote:
> "Eeyore" > wrote in
>
>
> > Don Pearce wrote:
>
> >> DigitalSignal wrote:
>
> >>> We are looking for the guidance of the digital
> >>> implementation of A, B and C weighting in the sound
> >>> level meters. Can anybody provide one or pointing to
> >>> the right direction? Thanks a lot.
>
> >> The equations for the functions are all here
>
> >>http://en.wikipedia.org/wiki/A-weighting
>
> > How easy is it to convert that into DSP code ?
>
> I understand that the usual approach involves Matlab.
>
> The usenet comp.dsp seems to be alive and well, if you catch my drift.

or any of a large number of other programs
http://www.dspguru.com/sw/tools/filtdsn.htm

you can try an eval version of QED2000. It is a very good way to
learn about DSP based filters.

http://www.mds.com/products/product.asp?prod=S004%2DW%2DSFX

In a nutshell, for an FIR filter anyway, the coefficient values simply
ARE the impulse response. And you go from frequency response to
impulse response via the FFT. And the programs use FFT to convert a
frequency response to an impulse response which then is basically the
coeffs. IIRs are a bit more difficult.

It's pretty interesting,,, play with it..

Mark

[Joe Kotroczo]

On 21/12/07 6:36, in article
,
"DigitalSignal" > wrote:

> Joe, thank you for your excellent description and guidance.
>
> We recently released a handheld dynamic signal analyzer (www.go-
> ci.com) with excellent dynamic range. Hopefully it can be converted
> into a sound level meter. But I wonder if sound level meter needs 8
> channels. It seems most of them just have one channel.

Depends on what you want to measure. Most handheld meters are designed to
measure an acoustical source, with one microphone, so they have one channel.

I would have thought that the weighting curves would be an interesting
feature in a signal analyzer, not only in a sound level meter.

--
Joe Kotroczo