[FFmpeg-user] Multiply audio samples

[Paul B Mahol]

On 9/15/18, Michael Koch <astroelectronic at t-online.de> wrote:
> Am 15.09.2018 um 09:33 schrieb Gyan:
>> On Sat, Sep 15, 2018 at 12:13 PM Michael Koch
>> <astroelectronic at t-online.de>
>> wrote:
>>
>>> Which other filter can I use to convert the input to -1..+1 interval,
>>> and convert the output back to 16bit or 24bit interval? I saw that the
>>> multiply filter in sox has these normalizations already included.
>>>
>> The aformat filter will allow you to convert between integer and floating
>> point formats.
>
> That's not what I mean.
> Let's assume I want to multiply two 16-bit audio samples. The interval
> is [-2^15 ... +2^15].
> After multiplication  the interval would be [-2^30 ... +2^30], which is
> not a usable interval for audio samples.
> That means I must either divide the result by 2^15, or I must convert
> the inputs to the [-1 ... +1] interval before multiplication, so that
> the result is also in the [-1 ... +1] interval, and then multiply by 2^15.
> My question is how to make this multipliaction or division by 2^15.

Filter inputs will be auto-converted from any non-float formats to
float or double one.

Float/double formats are in [-1 .. +1] interval.