Studio diary: practicing the basics!

[pask74]

Am I right to be mostly concerned by those dips in the lows and low-mids?

I've put thin plastic under the cloth everywhere, is this the reason for those lively high-mids and highs?

[pask74]

A noob question I probably should have asked first : is it ok to measure with a mono speaker aligned with the measurement microphone?

[pask74]

I just made 2 measurements:
One without the plastic sheet on the front left basstrap
One with it.
It seems that the 3k-9k range is slightly affected by this change (RT lenghtens).
What do the specialists say?
Is that a bad thing that the upper mids and highs are a bit more lively than the mids and low-mids?

vocal academy may 15 - front left bass trap without plastic sheet.jpg

vocal academy may 15 - front left bass trap with plastic sheet.jpg

[Soundman2020]

I tried to post the mdat file but the forum wouldn't accept this format, I'm afraid...

MDAT files are too big for the forum. You need to post them on a file-sharing service (eg Dropbox), then post the link here.

- Stuart -

[pask74]

OK - fine.
Is this GDrive link working?
https://drive.google.com/file/d/0B6wx2y ... sp=sharing

[Soundman2020]

Is this GDrive link working?

Yep, that link works fine.

However, the data in your MDAT file is suspect. According to that, you did the test at a level of about 140 dB If that were, true, you'd be dead. Also, the data only goes up to about 15 kHz, and at around 1 kHz the sound dies away normally for around 300 ms, then suddenly comes back up again after about 500 ms! That is impossible. the RT60 shows that the decay time is under 100ms at 300 Hz, but increases drastically to nearly 300 ms at 6kHz: that is pretty hard to explain, unless you have some very large tuned traps in the room.

And there's only one test in that file: you said you did two tests, but the MDAT you sent only contains one test.

So I suspect something is wrong with your test procedure, or your test equipment. I would start by repeating your calibration procedure again, to make sure that the readings are at least realistic.

What mic were you using for that test, where was it located in the room, and what speaker did you use for the tests?


- Stuart -

[pask74]

Hi Stuart, thanks for your reply.

Here is this morning's measurements: https://drive.google.com/file/d/0B6wx2y ... sp=sharing

Test level: it was a bit too loud (the speaker was saturating a bit), but never at 140db as I could stay in the room while the sweeps were playing. I've adjusted it for this test.

The lively (high-)mids is one of my concerns, actually. It's something I can even hear just while talking in the room.
I've put a plastic sheet under the cloth, as advised by John to preserve the higher frequencies. It actually does but also seems to lenghten the RT of those frequencies quite noticeably.
There are no tuned traps whatsoever in the room, unless those cavities in the ceiling (see early pictures on that thread) could be seen as tuned (which I doubt, as they are open)?
Am I missing something here?

[pask74]

OK, so I wanted to understand more what this plastic layer is doing to the sound, so I removed the upper half of it on the left wall. Here are the results:
https://drive.google.com/file/d/0B6wx2y ... sp=sharing

I can clearly see that the highs and high-mids are being shortened - am I right?
If so, I may well have to remove at least a good portion of this plastic sheet... (sob).

Any other impressions?

PS: I checked the levels again and they seem to totally fine. I'm not sure why REW indicates such high SPLs?

[Soundman2020]

I'm not sure why REW indicates such high SPLs?

Did you follow the complete calibration procedure? You have to tell REW what the real level is in the room by measuring it with a good quality hand-held sound level meter (not an iPhone app!) then entering that information into REW. It is part of the calibration. If you don't do that, then REW has no way of knowing what the actual SPL level is, and can only take a wild guess.

After you calibrate, you should then run the tests at about 80 dB per individual speaker, so you should be getting about 85 dB with both speakers and the sub all working at once, or about 83 dB if you don't have a sub.

What mic and speaker are you using for these tests (make and model), and where is the mic located?

Some photos of the room would help greatly to understand what is going on.

I can clearly see that the highs and high-mids are being shortened - am I right?

No. The two tests were done at different levels: the second one is about 5 dB higher than the first, so you cannot validly compare the two.

After your system is calibrated, you must ALWAYS do all later tests at exactly the same level, and with the mic in exactly the same position in the room, highly accurately located to within a few mm, every single time. If not, then you cannot compare measurements.

I'm still highly skeptical of the data in that REW file: I find it hard to believe that your RT-60 time increases so drastically in the highs, and drops to a minimum in the low mids: that makes no sense. I also find it a bit hard to believe that the speakers are showing almost flat response at 20 kHz. Please increase the upper limit to 30 kHz. next time you measure: I'd love to see how it is doing up there. You'll also need to increase the sampling rate of your sound card to be able to do that, but it will be worthwhile, I think...

What are the dimensions of the room?


- Stuart -

[pask74]

Hi Stuart,

Mic: Behringer measurement microphone (the famous one lots of people seem to use). It's located at 38% of the length of the room from the front wall.
Speaker: http://www.psiaudio.com/product/active-monitors/a17-m
Preamp: a Neuman-type console from the 90s.
Converters: Black Lion Audio modified MOTU HD192

I calibrated the soundcard by recording a loop but did not use the SPL meter, etc. - I need to do it first thing on Monday? Thanks for flagging this out.
I have a proper SPL meter in the studio so that shoudn't be a problem.
Sorry for this bad start.

Now, I can clearly hear those (upper)mids when just talking in the room, so unless it's purely psychological, what I see on the graphs in the mids kind of makes sense with my impressions when in the room.
Anyway, let me calibrate REW completely and run new measurements.

Currently, I only use 1 speaker, should I go for a stereo setup right away?

[stevev]

According to that, you did the test at a level of about 140 dB If that were, true, you'd be dead.

I don't mean to de-rail your thread here, but I did find that comment quite amusing as I've done the REW tests for my room without proper REW calibration as well well said Stuart.

[Soundman2020]

I don't mean to de-rail your thread here, but I did find that comment quite amusing as I've done the REW tests for my room without proper REW calibration as well well said Stuart.

Well, maybe "dead" is a bit of an exaggeration, but you'd most certainly be deaf, and also in pretty heavy pain! You need more like 200 dB to actually kill you instantly, and some say that 160 can kill within a few seconds, but 140 sure is "waaaay out there" on the spectrum of "OUCH". And certainly isn't attainable in a home studio. Nor with any single loud speaker that I ever heard of!

With one exception:

worlds-loudest-speaker.jpg

... I don't think I want a pair of those in my studio...

- Stuart -

[pask74]

I try to avoid exposing myself to more than 92dB-ish.
Those h u u u u u u u u u ge speakers are just, well, American-looking to me

Room's size:
- depth 455 cm (but there is a window that is about 30 cm deep on the front wall)
- width 419 cm
- height 292 cm (but there are 22 cm deep cavities, as you can see on pictures in earlier posts).

Knowing that a symetrical design is crucial for the stereo image, I already know that this room can probably be good enough for production and very good for vocal classes, but my goal isn't to turn it into a 1st class mastering room.
Also, because of that, I decided to keep as much volume as possible in the room, which takes us almost within Bolt's zone. I would have had to sacrifice 30-40 cm of the width to be in the zone but it would have taken the concept beyond the targeted budget.

[pask74]

Pictures: here are some pictures of the latest progress (see earlier posts for older ones).

mur droite - tissu s.JPG

mur arriere - tissu s.JPG

The ceiling corner traps are not yet covered with cloth.

[Soundman2020]

Those h u u u u u u u u u ge speakers are just, well, American-looking to me

Yup! They are actually used by the USA armed forces to simulate the sounds of a battlefield, for training purposes....

Room's size: depth 455 cm - width 419 cm - height 292 cm

That's actually not a very good ratio: It fails one of the three "critical" tests used by the BBC to determine if a room can be used as a studio or not.

Also, because of that, I decided to keep as much volume as possible in the room, which takes us almost within Bolt's zone.

"Almost" inside the bolt area, really means "outside" the bolt area... Some acousticians would take that as cause for either rejecting the room, or doing something about the dimensions to get it INSIDE the bolt area.

I would have had to sacrifice 30-40 cm of the width to be in the zone

Or make the room 10cm longer and 10cm narrower ... That would get you in the bolt area, and turn the BBC "fail" into "pass"...

But anyway, it doesn't make a huge difference, and as you said, your goal isn't to make it into a world-class mastering studio, so it will probably be fine, after it is treated.



- Stuart -