Topic: Tascam DR-07 frequency response

[sasa999]

Did some quick tests with my DR-07
(REV v5 software)
1. Line input vs Mic input (Low gain, filters Off)
2. Mic input, low gain + filters
3. Line vs Mic input+ 40Hz filter (very similar results, only -5dB at 6kHz)
DR-07 have strange 5dB drop at 6kHz on mic input   
It have strange lower frquency boost (max at 25Hz) with filters Off.
Drop over 20kHz is my sound card (Creative Audigy Zs)
Tomorrow will try some tests through mics.

Updated: pictures deleted because was wrong setup. New ones posted below!

[Gutbucket]

The 6KHz notch and the fact that the mic input response is flatter with the 40Hz filter engaged is interesting.

Seems to me they should label the 40Hz HPF setting as flat and the absense of any filter setting a 80Hz boost!  Just my speculation, but perhaps they don't because the ~5dB bass boost and 6kHz notch may compensate for the response of the internal microphones.  A response test using the internal mics should confirm that or not.

I'd love to see a similar response graph for the Tascam DR2d, which many are using around here for it's ability to recorded mic and line inputs simultaneously to seperate files.  It also has adjustable HPF settings, but no 400Hz boost option.

[sasa999]

A response test using the internal mics should confirm that or not.

Tests with mics will be less accurate because I do not have damped room and referencs speakers. But any way I will do it for my interest.

[page]

The 6KHz notch and the fact that the mic input response is flatter with the 40Hz filter engaged is interesting.

Yes, that is the most interesting aspect of this. I'm not sure it's to compensate the internal mics since you could run the 40hz "filter" setting on an external mic (whether it's a HPF or just signal processing is a different issue). I wonder if there is something in the DSP that is inappropriately coded (whether mislabled or poorly thought out I don't know).

[Gutbucket]

A response test using the internal mics should confirm that or not.

Tests with mics will be less accurate because I do not have damped room and referencs speakers. But any way I will do it for my interest.

As an absolute measurement you are correct. 

The useful comparison would not be between the recorded response of the internal mics and that of a direct signal like you made today, but the relative difference between the internal mics and an external mic with a known response. Using a flat measurement mic that doesn't need any correction itself is best, but any mic with a known response works, since if it's response is 'known' it can be corrected for by inverting it.

It's not the raw recorded curves that matters, but the difference between them.  The response of the room and speakers would be the same in each measurement so that cancels out, similar to disregarding the high frequency roll off that may be due to the soundcard.  For that to work, it's important to keep everything else the same such as the placement of the speaker and microphones, distance between them, stuff in the immediate surroundings, other noises, etc.

[Gutbucket]

The 6KHz notch and the fact that the mic input response is flatter with the 40Hz filter engaged is interesting.

I'm not sure it's to compensate the internal mics since you could run the 40hz "filter" setting on an external mic (whether it's a HPF or just signal processing is a different issue). I wonder if there is something in the DSP that is inappropriately coded (whether mislabled or poorly thought out I don't know).

Sure, you can run the filter with an external mic and it will still reduce the relative response below 40Hz.  We now know the response with an external input isn't flat. It really just depends on if Tascam has possibly configured things so that 'flat' settings actually produce a flat response using the internal mics or not.  If so, that's cool that they made the effort to correct the response of their internal mics, though it sucks for people using external inputs to the mic-in jack. 

The other possibility is that when set to 'flat' settings the mic-input doesn't actually produce a flat response for either the internal mics or an external input, which sucks all around.. but can at least be compensated for somewhat by running the 40Hz filter for an external input (doesn't compensate for the notch though).

Only way to tell for sure is comparing the internal mic response to a known external one.

[sasa999]

Was tested Tascam dr-07 internal mics , mic capsules Panasonic WM61a and  Primo EM172 response curves
Used two different self made preamps.  First pre1 = with NE5532 and second pre2 on ssm2019
As reference WM61a capsule at line input. Some room equalization.
Levels are changed (mics are diferent sensitivity) for for easy compare.
Tests in my beadroom (so it is not for serious tests).
Legend:
pre1 = first preamp
pre2 = second preamp
mic in = conected to mic input
line in= conected to line input

 wm61a_2.jpg  tested wm61a mic with 2 diferent preamps conected to mic input (LOW gain) vs without preamp vs ref. wm61a in line input. Using peamp in mic input can boost frequencies over 6kHz, without preamp they are lost
wm61a vs em172 pre2 line in_2.jpg  em172 capsules have very poor high frequency response.  I am very disapointed for them. Will try make some modification. Maybe it will help .
Sorry my english

[Gutbucket]

Appears Tascam does compensate somewhat for the steeper drop in response below 200Hz of the internals with the 'built-in' low end boost of the microphone input.  The internals are cardioids I assume, which typically have a drop in response below 200Hz compared to omnis.  The boost is not nearly enough to bring the response up to flat at the distance the measurement was made (which I assume was outside the cardioid proximity effect boost region), but appears to be enough to make the slope closer constant below 1kHz. 

In any case, the main point is that anyone using an external input into the mic-in should activate the 40Hz filter if they want a flat response in the bass, even though that would seem counter intuitive to anyone who had not seen these tests.  The dip at 6kHz is more of a concern.

[Gutbucket]

I'm really wondering about the DR2d mic input response curve now.

What software are you using to make the response measruements?

[sasa999]

Room EQ Wiszrd v5
The best is external mic-preamp-Line input.

[Will_S]

I'm really wondering about the DR2d mic input response curve now.

Appears to be much flatter, and ~identical line-in and mic-in, unless I did something wrong:

http://taperssection.com/index.php?topic=149264.0

[Gutbucket]

Thanks Will!

Looks much better.

[sasa999]

in first tests was something wrong. strage small waves, smothing.
I make another one more careful. Grey line is my PC response curve. Audigy ZS is not very good. It have big high frq. drop   
I think DR-07 have flat response in 13000-20000+ Hz
Now lines is without smothing.

[Gutbucket]

Thanks for doing these tests, sasa999.

[Church-Audio]

I think you have some issues with your test setup. Do a test of your soundcard looped back input to output and post that.