Spectrum graphs of DRC123
Axes
- X axis - frequency
- The X axis show the logarithmic frequency in Hz, usually from
20 Hz to 20 kHz.
The short cut label k2 stands for 0.2 kHz = 200 Hz. See
number format below.
- Y axis - amplitude
- The left Y axis shows the amplitude response in dB.
It is used for all amplitude graphs identified by <
at the left of the label.
- Y axis - group delay for calibration
- The right Y axis in the calibration graph is the group delay in units
of the current
frequencies cycle time measured in degrees. I.e. a value of 90
at 80 Hz corresponds to 90 / 360 /
80 s = 25 ms (a quarter cycle). It is used for all delay graphs
identified by > at
the right of the label.
- Y axis - group delay for measurements
- The right Y axis in measurement graphs is the group delay in seconds.
If a Y value leaves the graph a line is drawn at the top or bottom
boundary respectively. So you can see whether the values are to high or
to low.
Numbers
All numbers are written in short scientific form to conserve space where
the SI prefix
replaces the decimal dot. E.g.:
2k = 2000
-k18 = -0.18k = -180
Graph labels
- <, >
- The angle brackets show whether the graph uses the left or the
right Y axis.
- L gain, R gain
- Amplitude of the left/right channel in dB using
the left Y axis.
- L delay, R delay
- Group delay of the left/right channel in seconds.
- L ph. del., R ph. del.
- Group delay of the left/right channel in units of
degrees of the current frequencies cycle time.
- R2L, L2R
- Cross talk from right to left/left to right channel in dB using
the left Y axis.
The values usually increase at higher frequencies because of the white
noise floor of your line input which has increased energy compared to
the pink noise of the reference signal.
The noise decrease with measurement time.
- Δ gain
- Difference between the left and the right channel in dB using the
left Y axis.
- Δ delay
- Time delay between the left and the right channel in degrees
using the right Y axis.
- L IM2, R IM2
- Second order intermodulations of the left/right channel. This is
the energy at frequencies that can be expressed as sum or difference of
exactly two other frequencies.
The values usually increase at higher frequencies because of the white
noise floor of your line input which has increased energy compared to
the pink noise of the reference signal.
Boundary graphs
In addition to the dark graphs most views also show boundary graphs in lighter
colors. Most measurements are noisy and the boundary graphs show you
the minimum and maximum values that contributed. The dark graphs
show only average values. The detail level automatically scales with the
graph size.
Group delay
The group delay
is the phase change over frequency. The
absolute phase is mostly meaningless because of delays due to CPU
processing and sound propagation. But the phase changes are
significant
and contribute to the acoustical ranging. The average delay is shown as
text at the bottom of the graph. It might be different for the right and
the left channel due to path difference.
Indeterminate phase
Also at the bottom of group delay graphs there is an info about phase
unwrapping. Because the test signals from DRC123 are repetitive and the
impulse response of your room is non-repetitive there might be ambiguities
whether some response is from the current or the last cycle. DRC123 tries
to identify and count this ambiguities. The less the better.