6) Agora você deseja medir o nível de som

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Espero que você tenha lido a postagem chamada Noções básicas: Áudio (som), Parte 1 e Parte 2. É bom ter um conhecimento básico de frequências e caixas de som e cercar e amplificadores e nível e Loudness. Hopefully you have noticed some of the many ways that the human hearing system has made things “interesting” in normal life, maybe even pointed things out to people while you walked around your cinema auditoriums since learning more about these things.

Para nossos testes, vamos nos concentrar em um aplicativo simples e gratuito para iPhone e iPad da Apple, Volume dB. É de uma empresa chamada dsp mobile. Clique nestas palavras para o link de download do iTunes. There are many sound pressure level meters available, but this one has all the features we need, and is very simple to use…meaning, not only is everything that we need to see on the front screen, the ability to make changes is there also.

People may report back to you that there are internet sites that say that iPhone or other phone apps are not very accurate. That may or may not be true, but we don’t care. We just want a tool that is repeatable. Why? Because we are only interested in any changes that might happen from day to day, or week to week. Set-up engineers can worry about calibrated tools and measuring from 5 spots in the room, and other complicated things.

We only have to worry about doing the same thing each time we visit the auditorium and being able to communicate what we find effectively. What follows next is How To Do Those “Same Things”.

db_meter_screenshot_with_notes

A beleza do Volume dB is that the controls we need are on the same page as the meter itself. We don’t have to go to an Preference page, then back to check that our setup is correct, or to change it. When a light and color test tool does the same thing, there will be angels singing.

Etapa 1 _ controles.

Response ‘slow’ is what we want. Why? That is what the clever engineering types at the Society of Motion Pictures and Television Engineers have figured out, is the best answer. Generally, the reason is that we need to get a nice response from the meter that captures a stable range of the sounds, at all frequencies. If we used ‘fast’ the readings wouldn’t be as consistent from visit to visit. Click through to ‘slow’.

The same is true for ‘weighting’. We want to use ‘C’ weighting. Why? If you use ‘Off’ (which is sometimes called ‘Z’), or ‘A’ or ‘B’, the low frequency measurements will be lower and more inconsistent. So, click to ‘C’ on the 2nd button. Very important.

‘hold’ controls the Peak Number on the bottom right. Peak readings are valuable for some things, but not so good for measuring a cinema theater. Why? Because the design of the cinema auditorium is made to be a balance between hard and soft surfaces. Hard surfaces make too many reflections and distort the sound. To many soft surfaces, like the seats and the people and some of the wall treatment, and the sound will be dull. Peak readings measure the first clap of the thunder very well, but they don’t measure the average sound pressure level of the extended time of the thunder in the room. We want that averaged number.

Se você fuçar na internet, algumas pessoas dirão que 85 dB prejudicam sua audição. Sim, após 8 horas nesse nível, sua audição pode ser prejudicada. Mas a maioria das pessoas pode tolerar níveis muito mais altos sem danos durante um filme de 2 horas. Mas, como você pode dizer aos seus clientes, se estiver muito frio em nossos quartos, traga e vista um suéter. Se a realização desses testes estiver muito alta para seu conforto, traga e use alguns protetores de ouvido.

Finally, on the front panel is ‘Leq’, which is a measurement that averages the sound for a longer period of time than we need. It is good for something, but not these tests. Leave it set at “off”.

Step 2 – Position
Acomode-se em sua posição de escuta.
Essa posição é 2/3 atrás da tela e centralizada na tela.

Most of the time “centered to the screen” is the same as being centered between the 2 side walls. But if the screen is not centered on the front wall (for example, if there is an exit door on the left that pushes the screen from the side wall), make certain that you are sitting in the seat that is in line with the center of the screen.

Como você calcula 2/3? E como você descobre o centro da tela?
The most simple way is to look up and count ceiling tiles. For example, if there are 12 ceiling tiles from front to back, 2/3rds is under the back line of the 8th tile. And if the screen is about 12 tiles wide, then along the line of the 6th tile will be the center. Now look behind at where the lens of the projector is – just about all the time it will be “beaming” from the center of the screen.

Don’t be psychotic about the exact place, just be consistent.

Step 3 – Comfort and Repeatability.
O importante é se acostumar com a área de transferência, a caneta e o iPhone. Em seguida, segure o iPhone em uma posição cerca de 20 centímetros acima do assento à sua frente. Porque lá? Porque queremos que o microfone fique em um local neutro. Se estiver muito perto do assento, ou de sua cabeça, por exemplo, o reflexo ou absorção mudará as leituras.

Turn your iPhone so that the microphone – which is at the end that you normally talk into – is facing up. The onscreen picture will rotate. Get out your pen and make sure you can see the place on the page that you will be writing.

Finally, have a place to put down the iPhone. You won’t be using the sound pressure level measuring tool, dB Volume, until the end of this process. Until then, you will use your ears and eyes to judge things.

So. Are you comfortable? There will be some light from the screen soon, but can you see in the dark? Do you need to turn on the light of your phone? (I found a pen that has a light at the point…works great.) Can you reach everything? Write the Auditorium Number and the date in the proper space on the Managers Report Form. Make a check that says which DCP is going to play. OK. That works. Let’s get busy.

Step 4 – Get out your radio or walkie and make certain your teammate has loaded the Playlist. We want to test everything in the chain of equipment, from the that runs one of the test DCPs for play through the media player and the projector.  Have them hit Play.

Step 5 – Watch the scale on the right side of the screen when the bell tones and the pizzicato string tones go by. The bar will go up, move around the scale a little bit, then go down.

Vai ser preciso um pouco de prática e um pouco de talento para saber qual é o nível de pressão sonora desses sons.

But one thing is more simple and quite a bit more important – Silence. We want to measure silence. Then write it down. Then compare it to previous Sounds of Silence in that room.