For the same signal i have a difference recorded of 17.5 dB for these two recorders, it could look like the 12dB mentioned in article below due to the relation between dBu/dBFS. My brain says that stored files should be the same if same gainsettings are used with same mic. Anyone agrre on this?
That's the thing I was getting at earlier: there is no fixed relationship between dBu and dBFS, unlike dBu and dBV (dBu - 2.22 = dBV). dBFS will vary from recorder to recorder. The maximum mic input for the 702 is spec'ed at 10 dBu and for the 70D at 0 dBu, so, ostensibly, that should translate into a 10 dB difference in dBFS right there (I say ostensibly because the relationship between the maximum input and 0 dBFS isn't always as straightforward as you might expect). There are very probably other differences in how the two recorders handle an incoming signal of a given voltage, as well.
Now that you have an idea about how the two compare, why not just adjust the gain settings prior to, or after, recording to account for the difference?
Thankyou Aroonji for taking your time on this.
The reason it is aproblem for me is of course that I use recorder for something it was not intended for.
Let me give you an example:
I want to verify selfnoise for the recorder and for my capsules. For the capsules I could use an amplifier and a voltmeter, but for the recorder it is abit more complicated as you have no access internal to analog amplifiers but have to rely on internal digital processing.
With Tascam I have a display calibrated to dBu where max display is 0 dBu which is also the clipping level an therefore no over head is built in (as far as I know).
With Sd it is now clear that display is calibrated to dBFS where 0dBFS is dBU + 20dB or 0 dBu is equal to -20dBFS.
If you use recorder in a normal way you may set your amplifiers to show signal at let us say -16dB, that would be -16dBu with Tascam but with SD it would be -16dBFS which is not the same (+20dB) as Tascam.
If you record a file and on both and take the file into Audition or similar you would see that files are identical despite that they were recorded with different gain settings. This has now been verified by SD support that this is how Sd is calibrated.
My problem is that I use recorders to measure abolute (noise levels or signal) and get wrong results at verification because the dB's in audition are not the same as the the numbers stored in SD file (relative values).
I make a setup where a signal (or noise) is introduced to input amplifier at both items. I try to set same amplification 63dB (max) on Tascam and 63dB on SD. i would then expect the same output on both amplifiers before digitized.
If this signal was -63dbU Tascam would show max display and be near clipping but SD is showing -20dBFS (0dBu) which is ok sofar.
Problem for me is that the stored digitization is not calibrated to dBu but dBFS so when i compare the two files in audition, the file from SD is 20dB lower than Tascam file (same gain settings). i could of course compensate for this by adding 20dB amplification, but it is a bit worrying when small signals are used and whether you can trust the digital representation without degradation.
This has also ben verified by SD support to be correct, so that is how it is, but not very user friendly.
This confused me first because the selfnoise seemed to be far better with Sd than Tascam (could be), but when compensated for by 20db, suddenly Tascam seems to be very close to performance of SDxxx if measurement is considered reliable .
The first file attached is a screenshot from AUDITION showing Tascam 70d selfnoise (equivalent input noise) with input shuntet by 150 ohm resistance (resistor equ noise is 0,22uV/-130dbU) and max gain of 63 db which can be subtracted from measured value on output. Doing the same with SD would show a spectrum that is 20dB too low (absolute values) which should be compensated by 20db for comparing.
Second file attached is a screeshot showing spectrum from recorder noise measurement, red is Tascam and blue is SD702. Sd spectrum was compensated for as explained above.
If this measurement is considered reliable which I claim sofar, you may be surprised that Tascam has lower levels of noise at low frequency than SD from input amplifiers but overall is slightly worse but not that bad. (Input is 150 ohm resistor + 10uF) Interesting?