Mediciones (REW, Dirac Live, Audiolense, etc)

Iniciado por Deboi

Todavía no he podido escuchar los videos, mañana o haré. El UMIK-1 he leído por ahí que no es el más adecuado para usar fuera de lo que son extrictamente mediciones:

"With a USB mic like the UMIK, there is the issue of dynamic range - the A/D convertor in the mic allows for a very high max SPL input. For recording sounds well below that max, you are reducing the dynamic range of your digital signal".

Aunque también hay gente que lo ha usado con buenos resultados (incluso aplicando el archivo de calibración en Audacity):

https://www.minidsp.com/forum/softwa...ibrated-umik-1

Por desgracia parece que no se pueden descargar esos templates.

No creo que haya recortes en el margen dinámico en el que grabamos los videos. Las grabaciones suelen tener un margen dinámico real entre SPL pico y SPL promedio de no más de 15-20dB. Entre la señal más débil y pico máximo hay más diferencia... pero de nuevo limitado por el ruido de suelo del sistema (incluido ruido externo + coloración de sala y el pico máximo sin THD de la caja). Dudo sea menor que la que soporta un Umik




- Según el ruido de suelo (tras plantearse rumores) que midieron en Minisp, con el Umik-1 puedes captar cerca de 100dB de dinámica reales partiendo de sus 133dB máximos (eso roza el margen dinámico de un CD, que creo ronda los 96dB, que ya son mucho mayores de lo que da la mejor de las cajas en sala sin THD audible, restando pico de su "ruido de suelo"):



- Los rumores:

I'm definitely interested in buying one of those UMIK-1 microphones, but I've read a lot of concerns about their elevated noise floor (~50dB dBA, whereas other microphones in the same price range can do ~30dBA). To be fair this matches the specifications, which indicate max SPL at 133dB SPL and a noise floor at -74dBFS, which translates to an absolute noise floor of 59dB SPL. Nevertheless, I would appreciate being able to use the UMIK-1 to do THD measurements which require a clean, low noise floor.

I have the following questions:
Last time I checked, there was an issue with the noise floor being dominated by a nasty spike at 1kHz followed by its harmonics. Is this fixed?
What are the numbers regarding the noise floor for the recent revisions of the UMIK-1? I would greatly appreciate if people who ordered one recently could post a screenshot of what an RTA looks like in a very quiet room.
Is the UMIK-1 well-isolated with regard to USB power noise or should I be careful what I plug this thing into?
Does lowering the recording volume (i.e. in Windows) as any effect on the absolute (i.e. in dB SPL) noise floor? At first glance I would guess that the volume control is digital so it wouldn't have any effect, but I would sure like a confirmation.
It appears that you can open the UMIK-1 and change the sensitivity using DIP switches. Depending on the where the noise is coming from, lowering the sensitivity might, in theory, lower the absolute noise floor in the same proportion. I don't require high sensitivity (I would be fine with just 110dB max SPL), so that wouldn't be a problem.
Has anyone tried this? Does this tweak have any effect on the absolute (i.e. in dB SPL) noise floor?
Is it safe to do this with regard to altering the microphone - i.e. is there a risk of causing damage, screwing up the calibration, etc.?

Thanks in advance for your answers!

https://www.minidsp.com/forum/umik-q...66-noise-floor



- Las respuestas:

@ edechamps,

Just realized with this second post that we missed your first one! Sorry for that and thanks for your patience.. Let's try to answer your questions in order.

- Noise floor issue: that issue happened on one batch back in February. That's quite a while ago.. :-) This issue was fixed from the point we learned of the problem on subsequent batches (i.e. April).
- Noise floor would depend on your room. The fix that was done between the 2 rev was to remove the peaks.
- We haven't seen any issues on the USB power noise and effect of PC/Laptop of the past year that we have these..
- Volume control is digital and done at the driver level. The analog gain is done via DIP switches as you already noticed. Just open the mic and you can go up to 36dB of gain. That tweak has been done by quite a few especially on latest versions (no glue on body). You do have to be gentle when opening the ring though, it's not something you do everytime. You set it once and forget. It's not intended to be an analog gain control knob. You'll most likely damage the mic if you do it many times for each measurement. I don't see from the application we see (i.e. room measurement) why you'd have to change it often though.

Hoping this info helps.
Devteam

Just for your Info: I've performed some measurements in our anechoic chamber which has quite low noise (9dB(A) according to measurement with B&K 4179 1" ultra low noise microphone). The UMIK-1 was connected to a Dell Lattitude E6410ATG with SSD using REW and the supplied calibration file.



The A-wheighted noise of the UMIK-1 (700-0756) was 29.1 dB(A) and 43.1dB(unwheighted), which is both absolutely OK (a lower noise floor would limit the max. SPL). Please find attached the measured noise-spectrum.

http://www.imagehousing.com/image/music/1358290

If I will find the time i'll do some more tests including a comparison to a 1/2" measurement microphone from Microtech-Gefell and a calibration check with a calibrator (B&K Pistonphon).

Best regards, Daniel

https://www.minidsp.com/forum/umik-q...66-noise-floor

Dudo mucho que tu DR-05 puedan captar ese margen dinámico; con mi iM2 ya te digo que ni de coña (con la ganancia al mínimo para grabar señal que le llegue de máximo a 85/90dB, dudo tenga más de 50/55dB de margen dinámico con el pedazo de ruido de suelo que tiene. El Umik-1 lo supera con creces.

Un saludete