In most applications the LFE channel is designed to provide 10dB of additional headroom above the main channels, for low frequency effects, etc. This is accomplished by calibrating the LFE channel (not the bass-managed subwoofer portion of the main channels) so that it has +10dB of in-band gain above the main channels.

Most surround or bass-management controllers allow you to switch between 0 and +10dB on the LFE channel. The 0dB option is typically included for compatibility with sources that already have the +10dB boost on the LFE channel (such as with a DVD player, etc). However, if you are mixing or creating content, this is usually not the case, and in most cases it should be set to the +10dB position.

You can see how this works in practice by looking at the signal flow diagram of the Blue Sky BMC (follow this link).
(notice that the +10dB doesn’t impact the level of the bass-managed subwoofer portion of the main channels)

I hope this helps to clarify things further.

Cheers!

-Pascal

Thanks again .

If you want to confirm the LFE channel level is correct, you can route the 40 to 80Hz signal to the LFE channel directly, and it should read 95dBc, when the LFE channel is set to +10.

Again, it is important not to confuse the LFE channel with bass-management and the subwoofer. The LFE is part of the mix. Bass-management (like the crossover in a speaker) and the subwoofer are part of the monitoring system. Bass-Management should not be used to create a LFE channel.

For more information follow this link.

I hope this helps to explain it better.

Sincerely,

Pascal

thanks a lot!

If you are calibrating a bass-managed system; then when calibrating the bass-managed portion of the subwoofer signal and sending the 40-80Hz pink noise signal to any of the main channels (the center channel for example), you should measure 85dBc.

If you take this same test signal and feed it directly to the LFE channel, then it should measure 95dBc (or +10dB of in-band gain above the main channels).

Please note: In a Blue Sky monitoring system, which is bass-managed, the LFE channel is typically not calibrated separately. You calibrate the bass-managed portion of the subwoofer signal and then the bass-management controller adds the +10dB of in-band gain to just the LFE channel (which is then summed with the bass-managed portion and sent to the subwoofer).

If your system is not bass-managed: Then feed the 40-80Hz pink noise signal to the LFE channel input and you should measure 95dBc (or +10dB of in-band gain above the main channels).

It is important not to confuse the LFE channel, bass-management and the subwoofer. Follow this link for more information.

Feel free to e-mail me directly, if you have any additional questions: pascal@audiodesignlabs.com

Cheers!

Pascal

It appears that the reference level we are using for 0 dBFS is different from the reference level used by the manufacturers of some metering plug-ins by 3 dB.

We use the definition as specified by the Audio Engineering Society in AES17-1998-r2004, where 0 dBFS RMS is defined as the maximum digital value a 997 Hz sine wave can have in the system. Because the maximum value is defined using a sine wave, a square wave can theoretically have a maximum value of +3dBFS.

Because some metering plug-ins are defining 0dBFS RMS as the maximum possible amplitude for a square wave, instead of a sine wave, a sine wave will read 3dB lower on the RMS scale, but read correctly on the peak scale. These plug-in manufacturers are using a square wave as a reference because a square wave can cause overshoot in the digital reconstruction filters, when a 1kHz sine wave is used as the maximum digital value, which then causes clipping.

So based on this, we would recommend setting the reference levels, when using metering plug-ins that read a difference in level between peak and RMS levels, at -23dBFS on the RMS scale.

(from Rich Walborn – posted by Pascal)

With regard to our calibration level recommendations: These recommendations come from Dolby and are inline with current industry practices.

With regard to the calibration levels for the subwoofer: I believe you are confusing the LFE channel with the subwoofer and bass-management. We have an article on our website which addresses this common confusion. Follow this link for more information.

However, just to be clear, below are the levels you should use, depending on what you are calibrating and what type of test signal you are using:

Bandwidth limited LF test file (40Hz to 80Hz):
Bass-Managed Subwoofer Signal = 85dBc
LFE Channel @ +10 = 95dBc

Full-bandwidth Pink Noise:
Bass-Managed Subwoofer Signal = 79dBc (approx)
LFE Channel @ +10 = 89dBc (approx)

I hope this helps to answer your questions. Please let us know if you have any additional questions.

Cheers!

Pascal

I would be very careful using pink noise to EQ your system. The test signals above are designed to adjust the level of your system, including the relative level of the SUB.

In a small room, such as the typical recording studio, I would initially look at adding room / acoustic treatment, before I would look at adding EQ. Follow this link for more information.

If you are interested in adding EQ, then I would look for a time based analyzer, not just a frequency versus level analyzer. Something such as SMAART.

I hope this helps.

Cheers!

Pascal