I first thought that OL LEDs were reflected in the A/B OL LCD indicators, but it can happen that OL is lit while A/B LCD overload indicators are not.
The manual indeed states (p53) that OL can be lit while LEVEL is MIN.
I think OL logic is a bit more complicated, because there is
- OL LED per input channel (A/B)
- OL LCD bar per channel (A/B) (not necessarily linked with LED OL!)
- OL LCD bar per track (1-4)
Where exactly LEVEL intervenes is not very clear.
The DP-006 seems to store >0db data that Audacity will clip:
channel B of the recording was analysed.
some terms:
- A,B: channels (left, right)
- LEVEL: channel potentiometer
- A/B OL: LED that indicates input overload. initially this seems to correspond to the LCD OL indication above the A/B bars (but that is not true)
- track OL: horizontal bar in LCD above the track level, indicating some overload has occurred in the track
diagram events:
In following events, a synth was connected to A/B and its volume was turned down starting from its max level. A channel LEVEL was MIN, B LEVEL was MAX, DP-006 gain was high (to more easily trigger OL).
1- A+B OL: input overload, decaying RMS (input level is being decreased) shows DP-006 recorded volumes above 0db, Audacity seems to cut away that data.
Also, channel A LEVEL is zero(!), yet A OL is lit.
2- B OL lit
3- still B OL, but track OL off
4- B OL off
At this point, DP-006 amplifier is switched from high to med to low in order to get an idea of the different amplifier gains:
5- high gain: around -2.5db (as measured from the vertical scale, I have no idea how precise this is)
6- medium gain: around -8.5db
7- low gain: around -14.5 db. Note that here, although you can't see it in the diagram, input and track levels are touching the LCD "-12db" line. It appears to be difficult to modulate a signal's volume to hit exactly the "-12db" line, because of the low resolution of the LCD.
So the amplifier can boost 6db per stage (low->med->high)
In each of these gain settings, Audacity playback meter shows +0.5db from these values.
A bit further (around 3:30, not shown in the diagram), I put LEVEL at 50% and turn down source volume until track levels are around "-12db" line. and indeed, Audacity also shows (around) -12db.
Interestingly, input OL does not correspond to A/B OL indication.
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So I think the diagrams are of low quality. For example, the DP-004 (the previous model) is even worse, while the DP-008 seems more accurate.
