At 3:54 PM +1000 8/20/10, Paul Jacobson wrote:
>On 20/08/2010, at 1:24 AM, Rob Danielson wrote:
>
>> This suggests to me that the maximum available gain in
>> the 680's pre is around 52-55 dB.
>
>Hi Rob,
>
>The implicit assumption here is that the 702 has 68dB gain. This is
>not actually true. The SD recorders have around 48/50dB gain, rather
>than 68/70dB. This error has arisen because SD measure "input to
>-20dBFS" rather than the more commonly used "input to 0dBFS".
>Ignoring the "to -20dBFS" results in the gain being overstated by
>roughly 20dB.
>
>Raimund's tests include gain measurements which are measured "to
>clipping", rather than "to 0dBFS". Raimund might like to comment on
>the level difference between "to clipping" and "to 0dBFS" but my
>estimation is that "to clipping" results in 2-3dB lower gain
>figures? Raimund's "to clipping" tests indicate that in high gain
>mode the DR-680 has 12dB more gain (58dB) than the SD722 (46dB).
Hi Paul--
I do understand that gain measurement isn't as easy as one might
suspect and that the manuf. supplied specs are often lacking
sufficient criteria. 50 dB max gain for the 7XX's sounds very low
based on comparisons with SD pres rated at 66dB and other pres I use
regularly rated at 60dB of gain. The SD7XX is hotter than both. It
would be good to get some reliable numbers, but it doesn't impact my
test outcomes.
>
> > DR680 required about 14dB gain to match that made by the SD702. (Both
>> at max gain).
>
>The DR-680 has a low gain setting with 24dB less gain than the high
>setting, and therefore about 34dB gain (nb: this is confirmed by
>Raimund's recorder test page). I suspect Emil has used this lower
>gain setting for these tests, and the cumulative effect of a)
>overestimating the SD gain by around 20dB, and b) low gain setting
>on the DR-680, explains why you needed to apply 14dB gain to the
>DR-680 recordings.
Emil and I discussed using the high/max gain setting at length. I
believe he did because Paul D., Raimund and I found that the low
setting does introduce noise. I'll ask Emil again.
Assuming Emil did use high gain on the DR-680, my comment regarding a
possible limitation would probably still stand as its based on 7xx
max gain and the relative difference, whatever the gain numbers
actually are. :-) Rob D.
>
>cheers
>Paul
>
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