Strange input signal situation with BFD

**Wayne A. Pflughaupt** · **09-02-06, 06:20 PM**

I’ve been playing with the BFD I recently acquired from Sonnie, trying to get a handle on how to use the thing, and I've noticed something really peculiar: The level setting switch on the back (-10, +4) only seems to affect the meter! Running broadband pink noise through the BFD to the sub, I could not detect any audible difference with the switch in either position! Just to make sure, I whipped out the SPL meter, and it confirmed what my ears were telling me. I tried it with the "In/Out" light blinking (i.e. base input level) and steady-on (output level w/EQ). Same thing! The meter level changed, but no audible difference!

Anyone know what's up with this???

Regards,
Wayne

**JohnM** · **09-02-06, 06:26 PM**

Yep, it switches both input and output levels so your gain remains the same, you just shift the operating range.

**Wayne A. Pflughaupt** · **09-03-06, 03:21 PM**

Interesting. Since the +4 dBu signal is something like four times hotter (+4 dBu equals 1.23 Vrms, while –10 dBV translates to 0.316 Vrms), I would have expected at least some output differential...

Regards,
Wayne

**JohnM** · **09-03-06, 04:05 PM**

To look at it another way, the button changes the meaning of 0dB FS from 4dBU to -10dBV, so the external effects are only on the clip thresholds at the input and output.

**Wayne A. Pflughaupt** · **09-03-06, 04:46 PM**

Thanks John, I guess that makes sense. I’ve used plenty of pro gear, and home gear, but this is the first time I’ve really mixed the two, at least in my home system. Trying to get up to speed!

Regards,
Wayne

**Sonnie** · **09-04-06, 01:18 PM**

So, if I'm understanding this correctly... the only effect this switch would have is it could cause the input level settings to be inaccurate if we didn't have the switch set to -10dBV?

**brucek** · **09-04-06, 02:06 PM**

Quote:

the only effect this switch would have is it could cause the input level settings to be inaccurate if we didn't have the switch set to -10dBV?

But that's significant. In the -10dbV position, a max input signal is +2dBV (~1.26vRMS) and uses all the bits available in the ADC/DAC chain to define the voltage steps that results in the best dynamic range and S/N ratio.

Now feed the same signal and switch to +4dBU position. It expects a max signal of 16dBU (~4.89vRMS) for full scale use of the DAC with optimum dynamic range, but you are feeding it with a signal about 4 times lower than it expects.......

brucek

Advertisement