VU meters over network

[blue_luke]

Hi all, long time no see.
I am working on the most provocative/revolutionary/ advanced project in the world (off course!  ;D )

But seriously, i am wondering about the intricacies of sending say 24 channels of VU meters over a serial connection.
The questions I am asking myself are:
- what is a proper rate of refresh for a VU? 20 msec? ( i 've read that somewhere)
- Where the data comes from? an analogue to digital converter, a tap in the data stream from converters?

I own RME firewire 800 and lately a Firewire UFX. The software (TotalMix) has one VU per input/output/DAW channel
How do they do this.
Yes, you can go deep (very deep) if you know the answers to these questions.
Thanks, Luc

 

[JohnRoberts]

There are a few ways to look at this. TV picture refresh rate is something like 30 times per second so 33mSec. Refreshing at 50x seems pretty reasonable.

The ballistics (specifically attack time ) of real VU is probably slower than that, so you could probably push data even slower than that, if you added a smoothing algorithm to the receive end.

JR

 

[Richard Crowley]

What you mean by "VU meter" is undefined, but unless you are using something really super-extraordinary, you probably need only 8-bit (256-step) resolution for a visual indicator like a level indicator.  Sending 24 eight-bit words every 20ms is well within the capability of modern signaling systems such as I2C, etc.
I suspect that 50ms or even 100ms could be adequate.

OTOH, tapping into the digital audio stream is not quite so trivial, although some digital formats are easier to access than others.
Tapping in to analog audio would be easier for DIY, at least IMHO.

 

[abbey road d enfer]

But seriously, i am wondering about the intricacies of sending say 24 channels of VU meters over a serial connection.
The questions I am asking myself are:
- what is a proper rate of refresh for a VU? 20 msec? ( i 've read that somewhere)

If you really mean VU when you write VU, the attack time is normally 300 msec, so anything 10 times faster than that is more or less adequate, but if you need something faster like PPM, the refresh rate should be at least 2-3 times faster than the fastest attack time. Ther's no need to referesh at kHz rate because the reactivity of the eye is much slower.

- Where the data comes from? an analogue to digital converter, a tap in the data stream from converters?

We cannot answer this, because it depends on what you expect. In typical multitrack mixers, the signal can be sampled from several sources, typically group output, channel output, "tape" return. All these options have their justification.

I own RME firewire 800 and lately a Firewire UFX. The software (TotalMix) has one VU per input/output/DAW channel
How do they do this.

They tap it from different "points" in the DSP; at least that's what it appears to be from the outside. In fact the signal that is sampled is written into a momentary memory location and sent serially to be de-muxed and processed locally to be displayed.