Prom 32 - Audio Limiting (again) !

[johnb]

I've just seen that severe audio limiting was imposed on this Prom of the Bernstein Mass, but only to the actual performance - not on the announcer.

Exactly the same as was done to the opening and the Havergal Brian Proms last year.

I haven't noticed it on any other Prom this year (though that doesn't mean it hasn't happened).

[VodkaDilc]

I've just seen that severe audio limiting was imposed on this Prom of the Bernstein Mass, but only to the actual performance - not on the announcer.

Exactly the same as was done to the opening and the Havergal Brian Proms last year.

I haven't noticed it on any other Prom this year (though that doesn't mean it hasn't happened).

Having enjoyed that Prom in the hall, I was looking forward to both the R3 and the television repeat. I am technologically illiterate: are you saying it won't sound good?

[Dave2002]

Having enjoyed that Prom in the hall, I was looking forward to both the R3 and the television repeat. I am technologically illiterate: are you saying it won't sound good?

Is this coming round again? I missed both the Prom in the hall, and the broadcasts. It's gone from iPlayer now.

[Aubade]

I've just seen that severe audio limiting was imposed on this Prom

I too don't understand. Please explain (with apols to old timers who have ben there and done it before).

Thanks

[VodkaDilc]

Is this coming round again? I missed both the Prom in the hall, and the broadcasts. It's gone from iPlayer now.

Friday - R3 at 2pm
Thursday 6 Sept - BBC4 at 7.30

Information taken from the concert programme. I find that information about the afternoon repeats is not always easily accessible.

Don't miss it - stunning stuff!

[johnb]

The easiest way of explaining is to show a graphic representation of the sound levels during the concert:



As you can see the peaks have been uniformly limited (as it were 'chopped off') at approx -9.5dB. (The performance is the section between the orange verticals.)

This seems to be the default measure that the engineers employ when they have to cope with large forces.

As a comparison, this shows another Prom where limiting hasn't been employed:



(The middle section, between the orange verticals, is the interval talk.)

[Aubade]

Thank you johnb. Fascinating. Can I try your patience once more and ask why? Is it to avoid distortion on our variable quality receivers — tranny (in bathroom), stereo, tele, etc — or is there some other reason.

[johnb]

Aubade,

I might be wrong but I believe it is just a lazy method of dealing with larger forces. One of the issues the engineers face is setting the levels so that they don't exceed the maximum that can be coped with without distortion. If the levels exceed 0dB the peaks are clipped which causes distortion. With the general run of orchestral concerts they know more or less what to expect and so have the experience to know what the safe level settings are. With larger forces the easiest solution is just to employ dynamic range compression and/or limiting - which squeezes the audio range (this is what is used with FM, of course). A better solution would have been to carefully test out settings during the rehearsals and perhaps employ milder audio compression/limiting as a fail safe measure.

In this case, it appears that the compression/limiting has been done at source, so it is very probably that FM listeners would have had the delight of a double dose of audio compression!

If I am wrong - please, someone, shoot me down.

[Serial_Apologist]

Sorry to hear if audio compression is being applied again - I haven't been listening to Proms broadcasts, but had been given to assume from the consensus on another thread that the problem had been solved this year.

.Surely the problem could be solved by lower broadcast outputs, so listeners could make up their own minds by turning up their volumes. Or is the BBC wary of the noise abatement society? And why does not distortion not occur during the announcements?

[VodkaDilc]

So the over-powering climax which several of us have commented on towards the end of the Mass will be lost? Which will be the way of listening (FM. DAB radio, various TV systems) where we might hear it most "truthfully"?

Thinking back to the B Minor Mass (on both FM and digital TV later), I was conscious of getting a good listening setting (fairly loud) for the solos and quieter sections, only to be surprised that the massive choral outbursts did not have more impact. Is that a result of this sort of tinkering?

[jayne lee wilson]

I think I read that there was some amplification at this Prom? No excuse really, but maybe that's what they were scared of...
Sorry but I couldn't carve out the time for this one.

[VodkaDilc]

I think I read that there was some amplification at this Prom? No excuse really, but maybe that's what they were scared of...
Sorry but I couldn't carve out the time for this one.

Lots of it! And it seemed odd in the hall at first. But the ear soon adjusted.

[Bryn]

Thanks for the alert, John. I had not bothered to do anything with that particular Prom since Bernstein's Mass is not really my cup of tea. Outrageous that they are at it again.

[David-G]

John, Bryn, can I ask a couple of questions?

First, what effect on the sound will this limiting have? Will it be a form of distortion? Will it be very noticeable to the ear if you have not seen the waveform?

Second, just wondering what software you use to look at the waveform. If I bring it up in Audacity, will that waveform be the same as the one you are looking at? The vertical axis in Audacity seems to be calibrated differently.

[rank_and_file]

Johnb

The top plot in your interesting post 6 is (excluding the last bit from the studio) exactly what I get on Cool Edit Pro (now Audacity I think) but I had always understood that that was the result of the Optimod sound compression system in operation on the FM broadcast. The lower plot is the sort of waveform I see from CDs, LPs etc.

I was under the impression that the Optimod system was on 24 hours a day. But, as I type just listening after the prom, and my Cool Edit waveform is pretty similar to your lower plot, so, in my mind, the Optimod has been turned off.

Of course, I presume the Optimod limiting can be progressive as users of Audacity and its earlier names can easily control the sound volume input from a preamp by use of the Line In recording slider, the resulting waveform showing levels and any distortion, and adjust as required.

How does one get a double dose of Optimod? By at source, do you mean the recording venue? I seem to remember from a series of posts with Jonathan Swain a couple of years ago that the BBC studio monitors broadcast the sound before the Optimod compression got to it.