Re: [LAD] Suitable peak/RMS/etc. data for UI metering

On Mon, Jul 25, 2011 at 12:03 PM, Fons Adriaensen <fons@email-addr-hiddenwrote:

> On Mon, Jul 25, 2011 at 11:43:14AM -0400, David Robillard wrote:
>
> > */
> > typedef struct _LV2_PUI_Peak_RMS_Data {
> >
> > /**
> > The start of the measurement period. This is just a
> > running counter that must not be interpreted as any
> > sort of global frame position. It should only be
> > interpreted relative to the starts of other
> > measurement periods in port_event() calls to the same
> > plugin instance.
> >
> > This counter is allowed to overflow, in which case it
> > should just wrap around.
> > */
> > uint32_t period_start;
> >
> > /**
> > The size of the measurement period, in the same units
> > as period_start.
> > */
> > uint32_t period_size;
> >
> > /**
> > The peak value for the measurement period. This
> > should be the maximal value for abs(sample) over all
> > the samples in the period.
> > */
> > float peak;
> >
> > /**
> > The RMS value for the measurement period. This should
> > be the root mean square value of the samples in the
> > period, equivalent to sqrt((pow(sample1, 2) +
> > pow(sample2, 2) + ... + pow(sampleN, 2)) / N) where N
> > is period_size.
> > */
> > float rms;
> >
> > } LV2_PUI_Peak_RMS_Data;
>
> In all cases I know of the RMS value required for metering, dynamics
> processing, etc. is *not* the average over a period, nor over any other
> rectangular window. It is the result of applying a specific lowpass
> filter on the squared samples, which one depends on the application.
>
> This means that:
>
> * period_start: can be useful.
> * period_size: should be defined as the number of samples processed
> since the last event.
> * The definition of RMS as you provide it should be dropped.
>
> Ciao,
>
> --
> FA
>
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>

Hi Fons,

I'm interested in what you're saying about RMS metering. Could you give me
specifics or point me to a reference? I can't find anything by googling.
What sort of low pass filter is used for audio metering, for example?

Jeremy

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Received on Tue Jul 26 08:15:02 2011