Robert Eidschun wrote:I'm not sure how particular such sound systems have to be other than loud enough.
Cinema sound systems are certified for levels, frequency response, dispersion, isolation and so on. THX certified cinemas are particularly tightly controlled. You can find the specs on the Dolby and THX websites.
But that means that if I listen to the soundtrack on my home stereo, the quiet sounds sound somewhat too loud.
A perfect example of why the dynamic range control requirements are different for different reproduction systems in different listening environments. There is no 'one-fix-suits-all' solution. The Dolby Digital metadata (Dialnorm, DRC, downmixing ) is a very clever attempt to provide near-perfect results for different listening environments and situations, but it requires the production team to use it appropriately, and the home use to employ it in the approporiate situations. Many, like you, still avoid it and then wonder why they can't hear the quiet bits, or why the loud bits wake the babies!
Well, I assume that that is no longer an issue. It's hard to imagine that it would be in this day and age, given modern electronics.
Peak level control will always be required, whether the broadcast chain is analogue or digital (or hybrid). As long as analogue broadcasting continues (as it will here for another few years in TV, and indefinitely in radio), there will remain the need to prevent overmodulation, and digital systems must snever be allowed to clip, obviously.
The advantage of digital systems is that the alignment of different stages and interfaces becomes far simpler, but peak lvels still need to be monitored and controlled.
I'm not sure I follow here... Do you mean, "so that the home viewer no longer 'wants' to adjust the volume"?
No, I mean so they don't feel the need to adjust the volume between programmes or channels. In an ideal world, the home viewer/listener should be able to set the listening level they feel comfortable with and leave it at that for the duration of their viewing. They shouldn't have to turn it down when the adverts come on during the programme they are watching, or adjust it significantly when they switch to a different channel to watch a different programme.
...but this is a surprisingly difficult thing to achieve and is actually far more complicated than it appears. Some very clever peoploe in the EBU and other standards bodies have been trying to find ways of addressing it for years.
If there is some standard specified by the broadcaster that correlates sound pressure level to signal level, then there shouldn't be a problem.
There isn't and can't be. There is in the film/cinema world, because the replay environment is known and the signal level/SPL level can be defined and fixed -- that's part of the Dolby/THX spec.
But in the home environment, there is no fixed listening level. Some people listen loudly, others quietly. Some have noisy backgrounds to content with (eg, the kitchen ) and some need to keep it quiet to avoid waking the children. So in general, the dynamnic range must be kept relatively small. The BBC's own guidelines suggest maintaining dialogue within an 8dB range, for example.
So, for example, something like, "normal speach by a source within a few feet of the camera should produce average levels of around -x dBFS", or something like that.
That is done, as I said above. Normal speech would typically register between PPM4 and PPM6 on a BBC-style peak meter, which is roughly -18 to -10dBFS.
"+8 dBu" means that the voltage of the signal, v, is 8 db above 1 microvolt, i.e. +8 = 20 log (v/0.000001).
No. 0dBu is a reference voltage of 0.775V (RMS). So +8dBu is a signal level of 1.95V (RMS). The 'u' in dBu is derived from 'unterminated' and refers to the fact that modern audio interfaces are no longer the matched impedance types that were used up until about 40 years ago. Before then, the standard audio signal level was 0dBm where 'm' referred to the power 1 milliwatt. The standard citcuit impedance was 600 ohms, and dissipating 1mW in 600 Ohms produces a voiltage of 0.775V. Modern interfaces are voltage-interfaces, and we kept the same reference voltage.
Many US audio systems use an elevated reference voltage of +4dBu, or 1.223V (RMS).
But this specification is only meaningful in the analogue domain
Obviously, because it is an analogue voltage signal measurement.
How then can such a specification pertain to an audio signal that is represented digitally?
In the digital domain we use dBFS (dB below full scale), and the relationship between dBu and dBFS is set by the A-D and D-A converters employed. The EBU recommends an alignment of 0dBu = -18dBFS, while the SMPTE recommends +4dBu = -20dBFS.
Answer: the integral over that width.
Yes, pretty much all analogue meters are integrating meters. While the VU meter is intended to give some indication of 'avearage signal level' which has a vague relationship to perceived volume, the European PPMs were designed to give a much better and more reliable indication of signal peak levels.
However, a very deliberate engineering decision was made to prevent the meter from displaying fast transient peaks since even if these were allowed to overdrive transmitters, the resulting harmonic distortion products were too brief to cause annoyance, and leaving sufficient headroom to avoid transient overloads undermodulated the system very wastefully. To that end, European PPMs integrate over 5 or 10ms, and that's why they don't indicate fast transient peaks.
That was fine in the analogue domain, but is no longer entirely appropriate for the digital world where distortion caused by transient overloads in digital systems results in anharmonic distortion which is instantly audible, even when very brief. But the industry's familiarty with analogue PPMs ensures their continued use in many areas, and so the digital systems havea been engineered to maintain adequate headroom to prevent transient overload (as detailed earlier).
one might determine the average power of a varying signal, since changes in power (rather than signal amplitude) correspond more closely to changes in perceived volume.
This is true, but reliable determination of perceived volume is quite complicated, and a lot of work has been (and is being) done on finding a consistent way of metering perceived volume. Dolby produce a bespoke system for metering perceived loudness (primarily for the film industry) and a lot of broadcasters are now adopting the ITU Recommendations BS.1770 and BS.1771 for loudness metering. Meter manufacturers such as DK-Technologies and RTW already manufacturer suitable devices, and I think this will become the way forward in maintaining consistent programme and channel signal levels.
In practice, the PPM meter is probably much "dumber", not doing any calculus at all
I think you'd be surprised just how complicated the electronics of an analogue PPM is -- and there definitely is calculus in the signal processing.
I don't see how you won't end up with, as I pointed out, the rustling of clothing that's just as loud as footsteps, and in fact, that's what I've ended up with.
Rustling clothes can certainly be as loud as footstpes, or footsteps as quiet as rustling clothes -- it all depends on the clothes, the shoes and the surfaces!
But I take your point. At the end of the day it comes down to the skill and artistry of the dubbing mixer to balance the sounds as appropriate withing the dynamic range constraints of the medium he or she is working in.
The key is to maintain a consistent dialogue level, that matches the guidelines of the format, and then balance everything else around that, within the dynamic range constraints of the medium.
The problem is that the scene in question is a classical music concert, and I've set things up so that the loudest part of the music is at full scale (and would thus clip if any louder). Now, when the performers whisper, it's barely audible, as it should be.
I'll take your word for it. There is such a thing as a 'stage whisper' which gives the impression of whispering but remains entirely audible. There is little point in giving a performance where a proportion of the audience can't hear what is being said! And what might be barely audible in a cinema or oonn a hiigh quality dueatre monitoringg system will be completely inaudible when vieewed on a typical domestic TV. Hence the inherent need for skillful dynamic range control to suit the replay environment.
So, I raised the volume of the rustling clothes even more so, but now I'm back to having rustling clothes that are too loud with respect to the music.
No one said the art of audio dubbing was an easy one! Mixing (or at least regualrly checking a mix) on a comparative monitor system is essential until you have acquired sufficient expereince to know how a mic will translate from big hifi monitors to small TV ones. And mixing at low listening levels will also help to produce more appropriate and consistent results.
There seems to be no good solution in the situation that I've described here, unless you have any ideas(?).
It's a compromise, quite obviously. Some aspects of mixing perfection have to be compromised to produce a mix which is satisfactory when heard in a typical domestic environement on a typical TV. That's just the way it is. Skillful balancing can make that compromise less obvious, but it will always be there.
hugh
