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Internal mics of DR-40


Nosmo King:
The few times I've used the DR-40 internal mics, I've gotten the impression that their LF is rolled off.  Not surprising, I think, since the mics are purportedly cardioid.  Does anybody have an idea, or better yet some actual data, concerning the amount of rolloff?  I can't find anything in the manual, or by searching here.

Thanks much!

Cardioid microphones can have flat response down to 50 Hz or below--and 50 Hz is lower in practical terms than most people probably think it is. I doubt very much whether anything much below 50 Hz is coming out of the P.A. loudspeakers in a public performance space, for example. But it's rather unlikely that the microphones built in to a portable recorder would have flat response below 100 or so, because the main application for the built-in mikes in such recorders is speech pickup--recording business meetings or college lectures--and most of what a directional microphone picks up at low frequencies is room noise, solid-borne vibrations (shock), wind or air conditioning, breath noise, and generally garbage that only wastes headroom and detracts from the clarity of speech.

It may not even be the microphones themselves that are limited on the low end, but the electronics behind them may well have a low-cut filter built in. It would be nice if that could be switched off for serious music recording (= maybe 5% of the market) but the other 95% wouldn't know what to do with that switch, so presto, there's often no switch at all.

IOW the bad reputation that built-in mikes have for recording live music doesn't necessarily come from limitations in the frequency range of the microphones as such, but from the purposes for which the recorder as a whole is mainly designed. And built-in mikes are mainly for "quick and dirty" recording, mostly of speech, and mostly by users for whom convenience and simplicity are more important than sound quality.

Nosmo King:
Thanks for your reply.  I had always thought that cardioids could have good LF response.  However, in the past few years I have read comments in various places (including this forum) stating that cardioid LF is never as good as an omni.  I find this a bit puzzling.

You raise the question of *intentional* LF rolloff, either in the mics themselves or in the electronics.  I am aware that many handheld recorders (e.g. the Olympus DS series, the Philips series, etc.) are intended primarily for spoken voice.  However, the recorder in question seems to be intended for a musical or musician market.  (I base that on some features like XLR inputs, 4-track recording capability, overdub capability, high bitrates, etc.)  The recorder does have a switchable low-cut filter, but it was disengaged.  I'm not sure how much other *intentional* rolloff might apply to this unit.

I recorded a local band last week.  In the room, the sound was very boomy and muddy.  Using the internal mics (x-y option) the recording still sounded bass-heavy, but not as much as listening live.  That's what leads me to conclude there must be some amount of LF rolloff.  In fact, the recording sounded *better* than listening live.  This happens to be an atypical situation, though.  I was recording in order to give the band an example of how they sound from a position in the audience (which of course they can't hear from their stage position).  But because the recording is deficient in LF, it doesn't show them the extent of the problem.  In this case I actually want a recording that sounds worse (from a musical perspective) but more accurate.

Anyway, I don't have access to an anechoic chamber, and can't find any response curves online, so I would appreciate any further comments that others might have about this particular recorder and its mics ... especially anyone who happens to have an appropriate response curve.  TIA.

About cardioid vs. omni w/r/t bass response: When a condenser microphone is constructed as a "pressure transducer" then it can have essentially perfect response down to any frequency that you might choose. You could even go all the way to DC, but it wouldn't be wise, because such a microphone couldn't adapt to changes in barometric pressure and (for example) its capsule might burst if it were carried or shipped on an airplane. As a result all microphones that are built on this principle have a safety opening which limits their acoustical response to some frequency such as 1 or 2 Hz. Generally the circuitry of the microphone imposes a further low-frequency rolloff of some kind, which varies according to the intended application. Note that not all omnis are pressure transducers. Multi-pattern microphones that have an "omni" switch setting almost always contain a pair of back-to-back cardioids in one capsule head, and if so, their characteristics are generally somewhat different.

A low-frequency rolloff and/or other response reduction might be applied by design to the built-in microphones of a recorder even when it has XLR or other inputs which have flat response down to, say, 20 Hz. If directional microphones are built into a recorder, they will be sensitive to wind and solid-borne sound (e.g. handling noise, or noise conducted through the desk or table that the recorder is resting on), both of which occur mainly at low frequencies. No one would knowingly choose to record a serious music production via the built-in microphones of a typical hand-held recorder; it's widely understood that external microphones must be used for the highest quality sound. So we could both "be right" in that a high-quality recorder, designed to work well for serious music recording through its microphone or line inputs, might still have limited low-frequency response when the built-in mikes are used. A low-frequency limit makes sense as a "safety" precaution, while an overall reduction (for several octaves above the cutoff) of the low frequencies greatly improves the clarity of speech in reverberant and/or noisy environments.

The attached filter curves are those of the Nagra IV-S recorder, designed ca. 50 years ago by now. They are very well chosen from experience in dialogue recording for film. "S+LFA" is the curve that's used when recording speech in a noisy and/or reverberant space; it makes an enormous improvement in speech intelligibility without sounding "thin".

Finally, if you take a pair of cardioids that have good low-frequency response and a pair of pressure transducers with identical measured (on-axis) low-frequency response down to some frequency such as 40 or 50 Hz, and you make stereo recordings with both pairs in a normally reverberant space, the "feel" of the results--the sense of spaciousness--will still be very different at the low end. Partly this is because you would almost certainly space the omnis apart some distance and/or put an obstructing device between them (at least for the high or mid-high frequencies), whereas you might keep the cardioids close together or even "coincident" (a technique that IMO should be used only when a very high degree of mono compatibility is required).

But partly this is also because of the way that any directional pattern interacts with the "room modes" (low-frequency resonances produced by the room's rigid, physical boundaries); this even occurs in mono recordings and the effect was well known before the stereo era began. High-quality music recording in (say) the 1940s and early-to-mid 50s was generally done using a pressure transducer for the main microphone as much as possible, though good room acoustics are required for that to work well. Thus record companies were very choosy about where they would record their most important productions and the way in which the sound sources (instruments, voices) were physically arranged on the stage or floor. Directional microphones were regarded as "problem solvers" for dealing with inferior acoustics, problems of interference due to unwanted sounds, and/or special problems in balancing an ensemble.

Nosmo King:
Thank you.  That's a very good discussion.

I used a mono Nagra IV (as a recordist) in the early 70s, working with a 16mm filmmaker.  I never had my hands on a IV-S, although I always lusted after one.  I have a lot of respect for Nagra (i.e. Kudelski et al).  Before working as a recordist, I had been a tech in a shop that serviced Ampex recorders, among other things.  But I never learned much theory in that shop.  Most of the theory I know about magnetic recording was learned from thoroughly reading the manual of the Nagra IV.

I don't recall those EQ curves, but the M+LFA is especially interesting, with the partly-reduced LF shelf intended to reduce LF noise, without completely removing the desired LF part of the music.  Very smart, and IMHO very forward-thinking for those years.

I'm glad that you concur with my earlier belief that a cardioid mic *can* be flat down to a very low freq; it's all a matter of the designer's intentions.  I do find it interesting that I've been hearing the opposite lately, that a cardioid is not capable of good LF response.  Maybe that idea originated because some cardioids have the LF rolled off intentionally to compensate for proximity effect.  Anyway, I will revert to my previous belief that a card can go down quite low *if* designed to do so.

Thinking more about your comments re: reasons why a mic might intentionally be rolled off ... A cardioid will become less and less directional as frequency goes lower, so it will pick up highs over a narrow region, but LF over 360 degrees.  Therefore, when recording in the far field of a very reverberant space, the result might sound bass-heavy *if* the mic is designed to be flat on axis.

As to my present situation ... there is no way I can know what curve might be applied to the internal mics.  I don't have a schematic, so I don't know whether they are treated like the XLR inputs, or whether they have their own rolloff applied.  Within the 116-page manual, no mention is made of this, and no curves are given for the internal mics.  Apparently Tascam thinks this level of detail is unimportant to the typical user.  (By contrast, I just bought [at a yard sale] an old Ampex R-R *consumer* recorder from the mid '60s; the brief owner's manual includes a complete schematic.  Ah, the good old days...)

At any rate, you've restored my faith in the theory that a cardioid mic is capable of good LF response, if it's so designed.  I appreciate your time and the level of detail in your discussion.  It was a pleasure to read it.  I guess if I move some day to a new home, I'll have to be sure it has an acoustic anechoic chamber so I can test these things myself.  ;-)


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