On 19/08/2010, at 3:27 AM, Mike Rooke wrote:
> A is DR680, B SD702 - if A is the SD702 it has very poor rejection of 50h=
z mains or cabling issue? (9 dB at 50hz worse)
The 50hz hum is present in clip 1 (Recorder A) and 3 (Recorder B) but not =
2 (Recorder B) and 4 (Recorder A), so if Rob's labelling is correct (!?!) t=
his is environmental, not a recorder flaw.
>
> Considering both pre's are at max gain (thus exhibiting their lowest nois=
e) and the Mic is 8 dBA self noise? - the ticking clocks are +40something d=
B above the noise which may make it difficult to discriminate the noise, wh=
ich is below the mic self noise.
>
> Were trying to determine a 2dB? difference between pre's with 8 dB of mic=
self noise on top?
>
> From 300hz -1000hz, I measured just 0.349 dB difference between the recor=
dings. Above 10Khz its around 1.365 dB (Averaged from 2 second sections of =
the first two) - I'd assume the figures could be from slight gain level dif=
ferences in the recorders.
Looking at the steady 200hz tone that runs through all recordings, clips 1 =
and 4 were about 1.2dB down compared with 2 and 3.
I'd hesitate to make any assessment on mic preamp qualities based on this t=
est - however there is more energy below 200hz in clips 1 and 4 and this se=
ems to add weight to the ticks, but also muddies the sound slightly. I'll =
have to guess that recorder B is the SD702 as combined mic/preamp noise app=
ears to be slightly lower.
The theoretical difference between the DR-680 and SD702 with AT4022's is so=
mething like 0.25dB. Applying a-weighted eq in baudline indicates that thi=
s is likely to be the case - the difference in mic noise is very, very smal=
l. Without a-weighting clip 4 has a hiss that is biased towards the HF, and=
is more "aggressive" sounding that clip 2.
I'm probably wrong but there you go.
cheers
Paul
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