DP-24SD Mixer Block Diagram Question

[lastmonk]

I'm assuming??? that on the block diagram in between the ADC and the DAC we are talking about
the digital domain. But you know what they say about assuming.

The diagram shows that the faders goes from +6db to -inf . And the stereo fader goes from
0db to -inf.

I hear that in the digital domain things are based on DBFS. So since 0 DBFS is the ceiling, what is +6db referring to? Obviously not +6DBFS (no such thing right?) Or is this referring to the fact that inside the digital domain you can go beyond 0DBFS but you have to squash it down to 0DBF before writing out the actual wav file?

Sry for the rookie question here (but that's what us rookies do...) Should the +6db be considered as dbu or dbv rather than dBFS? If so why use that kind of unit if we're talking about data between the ADC and the DAC?

Somebody straighten me out LOL!

TIA

 

[Mark Richards]

That's an excellent question, lastmonk.

dBu, dBv, and dBV are power ratings. They are commonly used for audio equipment as a measure of the voltage (power level) a particular electrical circuit can receive or send without distorting.

dBu is an analog measurement.
Zero dBu (0 dBu) is in reference to .775 volts (i.e., 0 dBu = .775 volts).
(0 dBv and 0 dBV are referenced to different voltage levels.)

The pro audio (studio) standard is +4 dBu = 1.228 volts.
The home recording level standard is -7.78 dBu = 0.3162 volts.

Plus 2 dBu (+2 dBu) = 1.000 volt. If you look at the DP-24/32/SD Level Diagram in the OM, a +2 dBu Mic input level produces a 0 DBFS level after conversion to digital.

The Decibel is an analog measurement.
The decibel is a logarithmic measure. A sound with an intensity that is twice that of a reference sound corresponds to an increase of little more than 3 decibels. In common practice, the reference point of 0 decibels is the minimum threshold of hearing.

Because the decibel is logarithmic, there is no linear correlation between voltage and decibels.

DBFS is a digital measurement.
DBFS is "Decibels Relative to Full Scale". Full Scale is only relevant in the digital world. It is the point beyond which there is nothing but distortion. In the digital domain everything is 0 DBFS or less; there's no such thing as +3 DBFS.

There is no correlation/conversion of dBu to DBFS. The analog average power scale (e.g. a VU meter) is not equivalent to the digital peak scale (a DBFS meter). You can't match dBu and DBFS. dBu is volts; DBFS is a binary number.

(perhaps Phil or mj can double check me on these two tests, since my test gear is old and finicky)
Adjusting the track faders causes the digital value to change from "0" (infinity) to "127" (+6)
TEST 1
A 1kHz .775 volt (0 dBu) signal into Input A of my DP-24 with the Trim Knob set to unity gain (about the 1 O'clock position) produces about -6 DBFS on the Track 1 Meter; and with the Track 1 Fader set to zero, about -6 DBFS on the Stereo Master Meter with the Stereo Master Fader set to 0 DBFS.

Moving the Track 1 Fader to +6 raises the Stereo Master Meter to about -1 DBFS with the Stereo Master Fader set to 0 DBFS. (N.b. the track 1 fader has no affect on the track 1 meter.)

TEST 2
A 1kHz 0.3162 volt (-7.8 dBu ) signal into Input A of my DP-24 with the Trim Knob set to unity gain (about the 1 O'clock position) produces about -12 DBFS on the Track 1 Meter; and with the Track 1 Fader set to zero, about -12 DBFS on the Stereo Master Meter with the Stereo Master Fader set to 0 DBFS.

Moving the Track 1 Fader to +6 raises the Stereo Master Meter to about -9 DBFS with the Stereo Master Fader set to 0 DBFS. (N.b. the track 1 fader has no affect on the track 1 meter.)


Hope this isn't TMI and hasn't confused you further.

 

[-mjk-]

Very good explanation Mark!

When I use my console, I crank the input signal into the console until it peaks red and is right on the "hairy edge." Then I assign the channel to a group fader, and input that group out signal into the DP-32 at -12. Analog color at digital levels.

 

[lastmonk]

That's an excellent question, lastmonk.

dBu, dBv, and dBV are power ratings. They are commonly used for audio equipment as a measure of the voltage (power level) a particular electrical circuit can receive or send without distorting.

dBu is an analog measurement.
Zero dBu (0 dBu) is in reference to .775 volts (i.e., 0 dBu = .775 volts).
(0 dBv and 0 dBV are referenced to different voltage levels.)

The pro audio (studio) standard is +4 dBu = 1.228 volts.
The home recording level standard is -7.78 dBu = 0.3162 volts.

Plus 2 dBu (+2 dBu) = 1.000 volt. If you look at the DP-24/32/SD Level Diagram in the OM, a +2 dBu Mic input level produces a 0 DBFS level.

The decibel is a logarithmic measure. A sound with an intensity that is twice that of a reference sound corresponds to an increase of little more than 3 decibels. In common practice, the reference point of 0 decibels is the minimum threshold of hearing.

There is no linear correlation between voltage and decibels.

DBFS is a digital measurement.
DBFS is "Decibels Relative to Full Scale". Full Scale is only relevant in the digital world. It is the point beyond which there is nothing but distortion. In the digital domain everything is 0 DBFS or less; there's no such thing as +3 DBFS.

There is no correlation/conversion of dBu to DBFS. The analog average power scale (e.g. a VU meter) is not equivalent to the digital peak scale (a DBFS meter). You can't match dBu and DBFS. dBu is volts; DBFS is a binary number.

(perhaps Phil or mj can double check me on these two tests, since my test gear is old and finicky)
TEST 1
A 1kHz .775 volt (0 dBu) signal into Input A of my DP-24 with the Trim Knob set to unity gain (about the 1 O'clock position) produces about -6 DBFS on the Track 1 Meter; and with the Track 1 Fader set to zero, about -6 DBFS on the Stereo Master Meter with the Stereo Master Fader set to 0 DBFS.

Moving the Track 1 Fader to +6 raises the Stereo Master Meter to about -1 DBFS with the Stereo Master Fader set to 0 DBFS. (N.b. the track 1 fader has no affect on the track 1 meter.)

TEST 2
A 1kHz 0.3162 volt (-7.8 dBu ) signal into Input A of my DP-24 with the Trim Knob set to unity gain (about the 1 O'clock position) produces about -12 DBFS on the Track 1 Meter; and with the Track 1 Fader set to zero, about -12 DBFS on the Stereo Master Meter with the Stereo Master Fader set to 0 DBFS.

Moving the Track 1 Fader to +6 raises the Stereo Master Meter to about -9 DBFS with the Stereo Master Fader set to 0 DBFS. (N.b. the track 1 fader has no affect on the track 1 meter.)


Hope this isn't TMI and hasn't confused you further.

Excellent!!!!, This is not TMI It is precisely the level of explanation that works for me. Thank you so very much. I am curious what you used as input, to have this oscilloscope,multimeter accuracy LOL.

Your answer also helps me understand much better what the track faders are actually doing.

And the dBu being a volts thing and DBFS being a data (binary) thing I understand. But I guess part of my question was on the block diagram in between the ADC and DAC aren't we talking about data (digital stuff, binary,etc)?

I'm tempted to look at the block diagram as a flowchart of sorts, so when its referring to analog components I'm expecting things to be represented in volts, and when its referring to digital components I'm expecting things to be represented using data (DBFS) terminology.

And I certainly may be reading the diagram wrong. But why would Tascam label the fader with +6db (dbu) when we are already inside of the DP 24 and we're past the ADC and we haven't yet made it to the DAC? why not just say -1DBFS or something like that?

Is the diagram showing an Audio path or a Digital path, both, or neither????

Thanx so much for you answer. It has clarified a lot.

 

[-mjk-]

@lastmonk the answer to your question is, yes - between the converters it's all digital domain.

 

[lastmonk]

So if between the converters its all in the digital domain, why not describe the track faders in the block diagram as having some DBFS range (e.g -1 DBFS to -90DBFS)? I guess that's whats raising the question. Why use +6db to -inf when the block diagram is depicting something that is happening between ADC and DAC?

 

[Arjan P]

And I certainly may be reading the diagram wrong. But why would Tascam label the fader with +6db (dbu) when we are already inside of the DP 24 and we're past the ADC and we haven't yet made it to the DAC? why not just say -1DBFS or something like that?

Between ADC and DAC all is maths. So we're talking binary or hexadecimal calculations here, with the digitized audio that's converted to numbers. The reason a single fader can go over o dBFS is that the combined signals of more than one fader also go over 0 dBFS, so the calculator inside already has to be able to work with these 'high' numbers.

A short example: if you have two audio signals, digitized to a 16-bit number and they're both exactly at 0 dBFS, they will result in a +6 dBFS level. The digital mixer must be able to handle these calculations, so it needs better resolution (room) to work with - in this example with 16-bit signals, you'd usually see 24-bit resolution inside the mixer, or another mathematical 'trick' to work with these full scale signals (try Googling floating point calculations if you really want to know). Most DAWs these days work with 64-bit fp calculations for better precision.

Anyway, that's also why the master fader won't go over 0 dBFS, because here the audio must be translated back to analog and we must be back at the full level limit.

 

[lastmonk]

Its clear what scale is being represented when I look at the channel faders and master fader on my analog boards. I see the Tascam DP 24 as digital gear. I'm under the assumption that the scale being represented would be (data oriented) i.e. DBFS so the master fader topping out at 0 seemed to make sense. The track faders oth topping out a 6 did raise an eyebrow

Mark Richards answer sheds a great deal of light on this, but am I missing something here? Doesn't Tascam's documentation owe us just a little more explanation than what is shown in the block diagram, or is the track fader on a digital machine topping out a 6 a common ordinary, industry standard thing that any self respecting pro already understands

My current assumption (which again could be wrong) is that the 0 on the stereo fader is the 0 of the DBFS scale. But the 0 on the track fader is not. And the Tascam documentation is more or less silent on the issue. Unless of course you already understand the insider baseball of it all.

So is there a correlation between the scale markings on a typical analog board and the scale markings on the DP 24/32? For example right now just glancing at a couple of analog boards in my studio a Yamaha MG124 CX and a Yamaha MG10 both small portable boards.

MG124
The scale on the stereo fader is -30 to 10, peak
The scale of the channel faders is -inf to 10

MG10
stereo fader is -20 to 10, peak
channel faders -inf to 10

and unity falls in those scales.

On DP 24, stereo fader tops out at 0, and track fader tops out at 6. Upon seeing this I assumed the Tascam scale marketing for the faders were not representing the same thing as what's going on with an analog board. And the Tascam documentation is more or less quiet on meaning of their fader scales and meters.

 

[Mark Richards]

And I certainly may be reading the diagram wrong. But why would Tascam label the fader with +6db (dbu)

Adjusting the track faders causes the digital value to change from "0" (infinity) to "127" (+6). So, what Arjan said above.

Remember a decibel is just an analog ratio that represents the relationship of two analog sounds. A decibel has no intrinsic value. Doubling the sound level produces a 3dB logarithmic change of the second sound in relation to the first, regardless of what the actual first sound level is.

 

[lastmonk]

@Arjan P, understood., thanx much. Again you guys are explaining what Tascam should have made more clear in their documentation. So should the fader range in the DP mixer diagram be clarified to +6 DBFS (as an internal representation), or should the diagram just be changed to -inf to 0DBFS.

If the diagram means to show +6DBFS (for internal representation purposes) i.e. to deal with resolution issues, then are the Tascam people trying to convey this same idea on the Track faders that top out at 6?

So the stereo meter on the Tascam DP 24/32 is referring to DBFS and tops out at 0, and the track faders are also referring to DBFS and 0 is 0 DBFS and the 6 on the track fader is just trying to capture the notion of digital overflow?

 

[lastmonk]

@Arjan, @Mark Richards I get it now. Thanx much!!! Tascam could have done a better job documenting things. However, they've done a pretty good job with the block diagram for the new Tascam M 24

https://tascam.com/downloads/products/tascam/model_24/e_model-24_om_va.pdf

In that diagram its very clear what units of measure are involved and where. Its a pretty detailed block diagram. Maybe Tascam is getting better over time with providing detailed technical information. Or maybe the good work Phil Tipping did explaining the DP 24/32 through the block diagram made Tascam realize how useful these diagrams are to the community and they simply decided to do a better job when they released the M24. as a result of Phil's good work

Anyway thanx again. I now have a thorough understanding on the matter.

 

[Arjan P]

Yeah that level diagram is pretty good, actually very much like the one I know from the DM-3200. Which made me look that one up again, and there they give the digital domain a grey background - and even show two minimal levels: one at -168 dBFS for 24 bits and one at -192 dBFS for 32 bits (when calculating 24-bit signals).

 

[-mjk-]

@Arjan, @Mark Richards I get it now. Thanx much!!! Tascam could have done a better job documenting things. However, they've done a pretty good job with the block diagram for the new Tascam M 24

https://tascam.com/downloads/products/tascam/model_24/e_model-24_om_va.pdf

In that diagram its very clear what units of measure are involved and where. Its a pretty detailed block diagram. Maybe Tascam is getting better over time with providing detailed technical information. Or maybe the good work Phil Tipping did explaining the DP 24/32 through the block diagram made Tascam realize how useful these diagrams are to the community and they simply decided to do a better job when they released the M24. as a result of Phil's good work

Anyway thanx again. I now have a thorough understanding on the matter.

Or, (honestly) the Model 24 could be targeted at a more technically sophisticated market segment. Your typical home recordist wouldn't have asked those questions you did.

 

[-mjk-]

@Arjan P GREAT technical explanation, and I appreciate working in a second language myself. Nice job making it very understandable. We're glad you spend time over here in the DP forum.

 

[-mjk-]

@lastmonk btw, my Soundcraft Ghost's track and group faders top out at +10. But the 2-Mix fader goes to 0. One just has to keep it all in their head while mixing.

 

[lastmonk]

Or, (honestly) the Model 24 could be targeted at a more technically sophisticated market segment. Your typical home recordist wouldn't have asked those questions you did.

Yea, I get your point on the typical home recordist, but once you get to a block diagram that should be unambiguous because the average consumer will probably pass over the block diagram. but your point is well taken. And I know providing the right level of documentation is a tricky business. Other than the +6db to inf thing, I found the rest of the DP 24 block diagram fairly straightforward. But if you look at the block diagram for the M 24, Tascam makes the dBFS stuff explicit, with no beating around the bush

 

[-mjk-]

@lastmonk totally agree.