[opus] Overload Point for OPUS

[Marc Marroquin]

Hi Jean-Marc,

Thank you for the response!  I think you hit the nail on the head below.  The OPUS codec is all digital, so as long as you don't exceed the dynamic range (either 16 bit PCM or IEEE float) you are ok.

What I am interested in is the 'industry accepted' conversion to convert the signal between the digital domain level (using the term dBov or dBFS) that OPUS works in to the acoustic domain level (using the term dBSPL or dBPa).  Ensuring that the codec is mapped correctly is critically important to ensure that designers don't accidentally overload the codec (microphone -> OPUS) or overload the output (OPUS -> speakers or headphones).  

In the telecom industry we have standards, such as ITU G.100.1, that provides guidance to designers on how to map the analog domain <-> digital domain.  As an example, the G.711 codec (A law) has a defined mapping of > -3.01 dBov = digital overload.  If you exceed -3.01 dBov then the codec will overload.  Per ITU G.100.1 we map the digital level -3.01 dBov to a physical level of 0.92 dBV or 1.112 Vrms.  So a sine wave with a value > 0.92 dBV or 1.112 Vrms would overload the codec when that analog signal is passed to / from the codec.

I'm interested in what the corresponding 'industry accepted' mapping is of the digital <-> analog levels are.  Since OPUS is still quite new I cannot find any information on this.  Do you have any insight here?

Thanks!

-Marc
Mobile: 810-626-8935

> On Jun 20, 2014, at 3:04 PM, Jean-Marc Valin <jmvalin at jmvalin.ca> wrote:
> 
> Hi Marc,
> 
> It's not exactly clear how to define the an "overload point" for Opus.
> In normal use, it's not a good idea to go beyond the +/- 32767 values
> for 16-bit PCM or +/- 1.0 for float. That being said, internally Opus
> can represent signals that are up to about 48 dB louder than the PCM
> saturation point and if you use the float implementation you can
> actually encode and decode files that are much louder than +/- 1.0.
> 
> Cheers,
> 
>   Jean-Marc
> 
>> On 10/06/14 10:33 AM, Marc Marroquin wrote:
>> Hello,
>> 
>> 
>> 
>> Can you please tell me what the overload point is for OPUS in dBm0 or
>> dBV?  As an example, the G.711 A law codec has an overload point of
>> +3.14 dBm0 across a 600 ohm circuit. 
>> 
>> 
>> 
>> In ITU-T G.100.1 section 5.8 you can read more about the relationship
>> between dBm0 and dBov.  In that same section you can see that the G.711
>> A law, u law, and G.722 codec overload points are also defined.
>> 
>> 
>> 
>> Thank you,
>> 
>> 
>> 
>> *Marc Marroquin*
>> 
>> Telecom Account Manager
>> 
>> 
>> 
>> *HEAD acoustics, Inc*
>> 
>> 6964 Kensington Road
>> 
>> Brighton, MI  48116
>> 
>> 
>> 
>> Office: 248-486-0099 xt 226
>> 
>> Mobile: 810-626-8935
>> 
>> Web: www.headacoustics.com <http://www.headacoustics.com/>
>> 
>> 
>> 
>> 
>> 
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