# Audio frequency

Started by April 5, 2005
```Hi,

I have some questions in the basics of audio engineering as I am new to
this field. It would be great if somebody could help me out.

What is the format of 24 bit audio. How does it represent the frequency
and amplitude information?

Is there any relation between audio frequency and the number 1.3652125?

How do we determine amplitude from frequency..

Thanks...

Mahathi

```
```mahathi wrote:
> Hi,
>
> I have some questions in the basics of audio engineering as I am new to
> this field. It would be great if somebody could help me out.
>
> What is the format of 24 bit audio.

To my knowledge there is no standardized format, which means that each
manufacturer gets to choose its own.  In general the number
representation will just be some form of signed binary, with 2-s
compliment being by far the most likely.

> How does it represent the frequency and amplitude information?

Simply as a time-domain sequence of samples.
>
> Is there any relation between audio frequency and the number 1.3652125?

Or 42?  Not to my knowledge.
>
> How do we determine amplitude from frequency..

Without more information you don't.  In general they're independent
variables.
>

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
```
```Thanks Tim...

Do you have any idea as to what other information might be required to
obtain the amplitude....once we have the frequency...

Mahathi

```
```On 5 Apr 2005 11:26:09 -0700, "mahathi" <mahathi.choudhry@gmail.com>
wrote:

>Thanks Tim...
>
>Do you have any idea as to what other information might be required to
>obtain the amplitude....once we have the frequency...

As Tim said, they're independent variables. Knowing one doesn't
tell you anything about the other.
In general, amplitude is fairly easy to measure. Make sure you look
at enough samples to cover at least one cycle of the signal, and look
for the maximum and minimum samples, then subtract the minimum from
the maximum to get peak-to-peak amplitude. This also presumes there's
no noise in the signal.

>Mahathi

-----
```
```Ben Bradley wrote:
> On 5 Apr 2005 11:26:09 -0700, "mahathi" <mahathi.choudhry@gmail.com>
> wrote:
>
> >Thanks Tim...
> >
> >Do you have any idea as to what other information might be required
to
> >obtain the amplitude....once we have the frequency...
>
>    As Tim said, they're independent variables. Knowing one doesn't
> tell you anything about the other.
>    In general, amplitude is fairly easy to measure. Make sure you
look
> at enough samples to cover at least one cycle of the signal, and look
> for the maximum and minimum samples, then subtract the minimum from
> the maximum to get peak-to-peak amplitude. This also presumes there's
> no noise in the signal.
>
>
> >Mahathi
>
> -----
Hi Mahathi,
I'm not too sure about 24-bit audio but as Tim and Ben said, usually
you get a sequence of amplitude values in the correct order , sometimes
you have two interleaved signals for stereo and things get a bit more
complex ( sometimes you get the common signal and a difference signal)
; often. if you're reading from a file, in the header you get given the
sampling frequency and some sort of flag  to tell you whether it's
stereo or not.
If you know what the sampling frequency was then you can work out what
the frequencies in the signal are.

That's exhausted my entire store of hearsay about audio formats - I'm
hoping that if I've made any huge errors someone will tell you about
them.
Best of luck - Mike

```
```Ben Bradley <ben_nospam_bradley@frontiernet.net> writes:

>    In general, amplitude is fairly easy to measure. Make sure you look
> at enough samples to cover at least one cycle of the signal, and look
> for the maximum and minimum samples, then subtract the minimum from
> the maximum to get peak-to-peak amplitude. This also presumes there's
> no noise in the signal.

I would be careful here to distinguish this type of peak detection from
"analog" peak detection (which can be done digitally). In other words,
the reconstructed analog signal may have peaks that are higher than
the digital peaks due to the interpolation.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124
```
```Mahathi wrote:
...
> Is there any relation between audio frequency and the
> number 1.3652125?

What an odd question. Google returns two results for that number, which
makes it a Google Crack [1]. Apart from that, 1.3652125 = 109217 /
80000 = 149 * 733 / (2^7 * 5^4). I don't see anything that relates this
to digital audio. Perhaps if you mentioned something about the origins
of this number we could say more.

> What is the format of 24 bit audio.
Search for AES3 digital audio format.

Regards,
Andor

[1] Google Crack: any string that results in exactly two search results
when entered in the Google search engine.

```