power spectral density and energy under 500 hz

Hi,

If i calculate the power spectral density of a speech signal using Welchs
method i get power/Hz, right ?
If i want to find power or energy under 500 Hz i just integrate(or square)
from 0-500 Hz?

If this is correct would it be the same if i low passed the signal at 500
Hz, and apply Welch?

Tommy,

On 1 Mar, 00:41, "stromhau" <strom...@stud.ntnu.no> wrote:
> Hi,
>
> If i calculate the power spectral density of a speech signal using Welchs
> method i get power/Hz, right ?
> If i want to find power or energy under 500 Hz i just integrate(or square)
> from 0-500 Hz?

You integrate, without squaring, the spectrum from 0 t0 500 Hz.

> If this is correct would it be the same if i low passed the signal at 500
> Hz, and apply Welch?

In principle, the two results *could* be the same, yes. In practice,
your low pass filter might have a non-unity scaling factor which
alters the signal energy, if not accounted for. Welch' method
uses certain scaling windows and averages, which also tend
to affect the exact numerical value of the PDS.

The ususal advice is to be a bit careful using Welch' method
if you want exact numerical values for the PDS. Welch' method
is better suited to get an idea about general sectrum shape,
rather than the fine details.

Rune

>On 1 Mar, 00:41, "stromhau" <strom...@stud.ntnu.no> wrote:
>> Hi,
>>
>> If i calculate the power spectral density of a speech signal using
Welchs
>> method i get power/Hz, right ?
>> If i want to find power or energy under 500 Hz i just integrate(or
square)
>> from 0-500 Hz?
>
>You integrate, without squaring, the spectrum from 0 t0 500 Hz.
>
>> If this is correct would it be the same if i low passed the signal at
500
>> Hz, and apply Welch?
>
>In principle, the two results *could* be the same, yes. In practice,
>your low pass filter might have a non-unity scaling factor which
>alters the signal energy, if not accounted for. Welch' method
>uses certain scaling windows and averages, which also tend
>to affect the exact numerical value of the PDS.
>
>The ususal advice is to be a bit careful using Welch' method
>if you want exact numerical values for the PDS. Welch' method
>is better suited to get an idea about general sectrum shape,
>rather than the fine details.
>
>Rune
>
>
>

Thank you for answering,

What method would you recommend for this problem?

Tommy,

On 1 Mar, 13:10, "stromhau" <strom...@stud.ntnu.no> wrote:
> >On 1 Mar, 00:41, "stromhau" <strom...@stud.ntnu.no> wrote:
> >> Hi,
>
> >> If i calculate the power spectral density of a speech signal using
> Welchs
> >> method i get power/Hz, right ?
> >> If i want to find power or energy under 500 Hz i just integrate(or
> square)
> >> from 0-500 Hz?
>
> >You integrate, without squaring, the spectrum from 0 t0 500 Hz.
>
> >> If this is correct would it be the same if i low passed the signal at
> 500
> >> Hz, and apply Welch?
>
> >In principle, the two results *could* be the same, yes. In practice,
> >your low pass filter might have a non-unity scaling factor which
> >alters the signal energy, if not accounted for. Welch' method
> >uses certain scaling windows and averages, which also tend
> >to affect the exact numerical value of the PDS.
>
> >The ususal advice is to be a bit careful using Welch' method
> >if you want exact numerical values for the PDS. Welch' method
> >is better suited to get an idea about general sectrum shape,
> >rather than the fine details.
>
> >Rune
>
> Thank you for answering,
>
> What method would you recommend for this problem?

What question do you try to answer? Do you want relative
power contributions from different bands of the spectrum,
or do you need exact numbers?

Rune

On Feb 28, 3:41 pm, "stromhau" <strom...@stud.ntnu.no> wrote:
> Hi,
>
> If i calculate the power spectral density of a speech signal using Welchs
> method i get power/Hz, right ?
>
>
> Tommy,

For correct scaling of welch for your choice of units take a look at:
http://www.bksv.com/pdf/bv0031.pdf
on page 29 for a discussion of Signals and Units.

Dale B. Dalrymple

>On 1 Mar, 13:10, "stromhau" <strom...@stud.ntnu.no> wrote:
>> >On 1 Mar, 00:41, "stromhau" <strom...@stud.ntnu.no> wrote:
>> >> Hi,
>>
>> >> If i calculate the power spectral density of a speech signal using
>> Welchs
>> >> method i get power/Hz, right ?
>> >> If i want to find power or energy under 500 Hz i just integrate(or
>> square)
>> >> from 0-500 Hz?
>>
>> >You integrate, without squaring, the spectrum from 0 t0 500 Hz.
>>
>> >> If this is correct would it be the same if i low passed the signal
at
>> 500
>> >> Hz, and apply Welch?
>>
>> >In principle, the two results *could* be the same, yes. In practice,
>> >your low pass filter might have a non-unity scaling factor which
>> >alters the signal energy, if not accounted for. Welch' method
>> >uses certain scaling windows and averages, which also tend
>> >to affect the exact numerical value of the PDS.
>>
>> >The ususal advice is to be a bit careful using Welch' method
>> >if you want exact numerical values for the PDS. Welch' method
>> >is better suited to get an idea about general sectrum shape,
>> >rather than the fine details.
>>
>> >Rune
>>
>> Thank you for answering,
>>
>> What method would you recommend for this problem?
>
>What question do you try to answer? Do you want relative
>power contributions from different bands of the spectrum,
>or do you need exact numbers?
>
>Rune
>
>

Hi,
I want to find the amount of energy below 500 Hz, so i guess exact
numbers.

Tommy,

This energy or power thing is one of many features i want to implement.
When reading paper on the subject(emotional speech) it is only mentioned
as energy under a value of hz(often 500Hz).
So the question is how can this be done ?

Tommy,

On 1 Mar, 23:03, "stromhau" <strom...@stud.ntnu.no> wrote:
> This energy or power thing is one of many features i want to implement.
> When reading paper on the subject(emotional speech) it is only mentioned
> as energy under a value of hz(often 500Hz).
> So the question is how can this be done ?

You have to search the literature on speech processing to see
what methods they use. There is likely to be some accepted
"usual" way of doing things. Post on one of the speech
processing newsgroups.

Rune