What is “Frequency Response” in Microphones?

This question comes up frequently in classes and through @justaskjimvo – though usually the question is more along the lines of “What microphone is best for my voice?”

My answer is often – “The one you are using right now…” because that questionable quest can become a serious time suck of diversion and A/B/C/D…etc. testing. If you end up spending more time reading microphone reviews or watching Microphone “Shoot-Outs!” videos than reaching out to clients or analyzing scripts, it might be worth evaluating that balance of effort.

But, mics do differ.  There are shotgun mics, condenser mics, ribbon mics, dynamic mics, side-address and top-address mics, different pickup patterns and more. Some are “warm”, have “cut-through” or tend towards sibilance.  All of those differences are outside of how we get a sense of the mic’s actual sound.  To figure that out, a good place to start is the microphone’s Frequency Response.

In non-technical terms:
The frequency response is how accurately the microphone captures input. If you do a little digging into the spec sheets for any microphone (most companies post this info separately on their site, or if not, you’ll typically find it in the pdf of the microphone manual), you’ll find a graphic of the frequency response curve.

Here is one:

The horizontal part of the graph refers to the frequency of the incoming sound – it goes from 10 Hz (very low) to 20 kHz (probably beyond the range of anyone to hear).

The vertical part shows whether the the microphone itself increases or decreases the level of the incoming signal. The incoming signal is nominally 0 dB (some microphone companies show this nominal signal at 10 dB or some other value – that doesn’t matter – what you are looking for is the difference between the incoming signal and what the microphone does to it).

Let’s break down that curve into three sections:

On the left-most section above, you’ll see the frequency response (red line) is less than 0 dB. That means that the microphone reduces the actual input signal (orange arrow). Where those arrows are pointing is about 30 Hz in the audio spectrum (just about the lowest key on a piano) and the frequency response is about 5 dB quieter than the source sound – that’s what gets “passed through” the electronics of the microphone.

In the center, you’ll see the much-desired (by audio engineers, anyway) “flat response” – the microphone neither increases nor decreases the input.

Above 3 kHz (3,000 Hz) – to the right of the dotted blue line – you’ll see that the microphone actually is more responsive to those frequencies. You see a “lift” of about 5 dB. Again, the orange arrow points to the input and the green arrow points to what the microphone will render.

As an example, if you have a voice that is a bit higher and thinner, it’s going to have more energy at a certain frequency range.  If your microphone tends to be more responsive in that range, it will enhance that pitch and timbre.  In other words, it’s going to emphasize the higher pitch and “thinness” in your voice.  That might steer you away from a microphone that responds that way.  Ideally, we want a true representation of how we sound as Voice Actors.

In fact, a high quality microphone may even sound a bit “flat” at first, because it’s not emphasizing any particular part of the frequency band. Audio Engineers tend to like that because all the audio information is there, and they can tune what they need.  With some microphones, parts are boosted, which tends to over-emphasize certain frequencies.  A similar example would be listening to music between quality Studio Monitor headphones  (which provide a flat output response) and a set of consumer-grade Beats headphones, which pump up the bass.  An engineer will have to offset that to make it sound right.

When you look at frequency response information, you’ll find a wide range of response characteristics. There are always tradeoffs between the mechanics of the microphone diaphragm and electronics, the quality of the microphone and what you what are hoping to do with it.

That means when you hear about the latest-greatest (or even the mic you “need” if you are a voice actor), take a moment to track down the frequency response information.

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