Flutopedia - an Encyclopedia for the Native American Flute

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Flutopedia Symposium

Selecting a Microphone for
Recording the Native American Flute

This page of Flutopedia was contributed by Barry Higgins of White Crow Flutes.

Any editorial comments that were added after Barry's original article appear in this tan box.

There is a lot of conversation regarding microphones for live play and recording with the Native American flute. With so many brands and models on the market the initial task of choosing one can be somewhat daunting. Before I go any further it is important that I make some delineations between microphones used for live sound reinforcement and recording. Although not highly recommended (for flute) one can record with either type.

The condenser type microphones used frequently for recording have greater sensitivity and frequency range over live dynamic microphones and generally produce a “flatter”, hence truer, recording. The condenser microphone can also be used for live sound but by their sensitive nature are fragile and susceptible to breakage, improper positioning, and they cost so much more to risk the rigors of the road. Some mics are positioned as “cross-over” microphones, which attempt to service both arenas and are often referred to as home recording or project microphone in the sales literature. The expectation of a “good” recording microphone is to record the “truest” sound. This means the tone is near as listening with the human ear without coloring the sound, or adding artifact or signal noise over the entire range of the instrument or voice. This would be referred to as “flat” sound.

Recently I had the opportunity to test a number of different microphones and record the sound for both audio and visual comparisons. My purpose here is not to make a recommendation of a particular mic but to give you the analysis of our work and, through that work, give you the working knowledge of how to choose a mic that might be good for you. The testing was more specific to recording that live play but results can be universally applied. The six microphones were of the “studio class” or condenser mics and one live or dynamic mic (specifications only) thrown in for a reference point. All adjustable pattern/response microphones were set to flat response and cardioid pickup pattern.

Polar Patterns

Cardoid polar pattern showing the sensitivity of a cardoid microphone based on angle. Significant dropoff of sensitivity to the sides, and near zero sensitivity behind the microphone.The diagram on the left displays the Cardioid’s pickup pattern by the green highlighted area. Notice the absence of sound pickup at the rear of the microphone. Using this type of pattern the diaphragm of the microphone should be directly facing the sound source to be recorded. Notice also as the direction of source moves laterally, starting with 30 degrees, the pickup ability begins to fall off and at 90 degrees falls off very sharply. This is important information when positioning the microphone and player (sound source).

By example, if you were to do a duet with this type of mic, you would not want either player 90 degrees to the diaphragm as sensitivity would be decreased while 30 degrees to the face the results would markedly improve the reception of sound. Many new or advanced microphones now include options to change the pickup patterns and thereby increase the usefulness of the product.

We tested the microphones specific to recording use with Native American flute, so keep in mind the results may differ with their use with other types of instruments. Wireless or Lavalier microphones were not tested but I will share my personal opinion on as a sidebar of these results at the end as well as my recommended method to mic a Native American flute. We recorded each microphone with three different range flutes: a Medium B4, a Medium F#4, and a Low A3. for each flute the same musical phrase was played and included a varity of long, short, incidentals, and expressive note effects.

The recordings were made on an all-digital system with the only exception of the Analog to Digital conversion at the Microphone to A/D processor. The recording were made using a Mark of the Unicorn (Motu 896) digital interface/converter, Digital Performer 3.1 DSP software, and a 500 mHz Mac iBook  computer under OS 9.22. The signal was recorded in 16-bit format and 44.1MHz using identical gain settings for all microphones and test recordings. The reason we used the same gain level was to identify how “hot” (sensitivity) the microphones would be on a comparative basis. The hotter a microphone is the greater the saturation of the signal on the recording. The signal was even allowed to “clip” if the signal was greater than 10db over the unity gain setting (balanced zero).

The microphones were attached to a tripod boom microphone stand using the manufacturer’s supplied attachment support. The diaphragms of the microphones were directed to the mid bore position of the flute (between holes 3 and 4) and was parallel to the angle of the flute. The proximity of the microphone to the bore was set at 1 foot from the diaphragm. As we were interested in overall performance we made no efforts to compensate for the length differences of the flute bores to the focus of the mic and the distances to the foot of the bore. The fundamental on longer flutes can often require a second microphone to pick-up the sound, as it is directed and further away from the pickup patterns of most microphones.  The following table lists the microphones tested in price rank order:

Manufacturer Model Retail Price “Street Price”
AKG C1000s $312 $199
Sennheiser MD421 II $485 $299
AKG C3000b $520 $299
Shure SM81 $530 $329
Audio Technica AT4050 $999 $599
Blue Blueberry $1,295 $999

This test had two distinct parts:

  • Objective – technical specifications and visual wave form review of the recorded frequencies, and
  • Subjective – how it sounded to me.

One’s choice in a mic should be a combination of both aspects. You have to get a good recording but you also have to like the sound.

Sound Frequency and Pitch

Note: this portion of the original article by Barry Higgins discusses the same issues as the Flutopedia Octave Notation page.

Before we get to the factory specifications I would like to give you some reference points of sound. Sound frequency is measured in Hertz (Hz). Below is a table that describes the pitch, frequency, Native flute frequency, and some reference notes. The pitches are described as a reference to the octave it compares to the full size piano. The Native American flute’s generally classed as Medium would be in the C4 fourth octave on a piano which means as in the case of a Native American flute C of the fourth octave most refer to this as a Low C but the reality it is of the fourth octave or Middle C.

Pitch Frequency NAF Fundamentals Reference Notes
C0 16.351 Hz   Lowest definite note of any standard instrument
E0 20.601 Hz   Approximate bottom of good hearing person
A0 27.500 Hz   Bottom note of a standard piano
E1 41.203 Hz   Bottom note of a string bass
E2 82.407 Hz   Bottom note of a guitar
G2 97.999 Hz   Bottom of typical male voice
C3 130.81 Hz Sub-Bass C Flute Lowest fundamental note of practical NAF
F3 174.61 Hz Sub Bass F Flute Bottom of typical female voice
C4 261.63 Hz Middle C Flute Middle C of a standard piano
D4 293.66 Hz Middle D Flute Top of typical male voice
A4 440 Hz Middle A Flute Often used as a reference tone
C5 523.25 Hz High C Flute Top of typical female voice
G5 783.99 Hz High G Flute Highest fundamental of practical NAF
C6 1,046 Hz   Highest written note for trumpet
G6 1,568 Hz   Highest top note of a practical NAF
C8 4,186 Hz   Highest note on a standard piano
B8 7,902 Hz   Triangles and Drummers Brushes
C10 16,744 Hz   Typical high end on good stereos
  20,000 Hz   Approximate top of good hearing person

As you can see in the chart above the range of the current scope of available Native American flute’s is quite narrow even over the scope of commercially available models.

Microphone Terminology

Below you will find some “lay” description of the specification terms, sort of a “mics for dummies” thing where the full descriptions might confuse the general point of this report. The specific data was taken directly from the manufacturers specifications sheets as posted on the manufacturers websites. I have found retailer information to be less accurate at times. If you have any question about sales materials always check out he manufacturers site before final decisions are made.

Frequency Response

Frequency Response shows us the mics ability to “pick-up” the sound within a specific range of pitches as measured in hertz. The first number is the lowest frequency or bottom end and the second number is the high frequency or top end. The human ears generally can pick-up sound in the range of 20 Hz to 20,000 Hz, which is only one one-millionth of one percent of the total sound spectrum.

Many people have undetected upper or lower frequency hearing loss, which can affect the total range they are able to hear. The Native American flute pitches fall in the lower half of this range so its potential for doing well with most microphone response is quite good. If your intent is to play or record other instruments you can see that the range must expand top and bottom to include instruments of low pitches like Bass guitar and Drums and to Highs like some percussive instruments like egg shakers, chimes etc. so keep in mind what you might want to include in a recording other than flute and make sure the mic can respond properly in the overall desired range.

Graph of Shure SM81 sensitivity based on frequency.

The diagram above is a plotted response curve for the Shure SM-81 condenser microphone. We will be dealing with the solid line on the response curve only at this time. As you can see the total response range of the mic is about 40Hz to 20,000 Hz, however printed materials state the range is from 20 Hz to 20,000 Hz. If we look at the graph the response (light orange) is quite flat (a good thing!) and begins to falls off at about 15,000 Hz. So we might say that the effective range is only 40Hz to 15,000Hz (medium orange). The other two dashed lines on lower frequencies show two other user selectable options for adjusting the low-end sensitivity of the microphone. These are used to decrease bass levels that can become “boomy” if not controlled. This mic has settings to start the “roll-off” at two separate frequencies.

Roll Off

Roll Off is the area on the graph where the sensitivity begins to decrease from flat response. This point in a response curve it maybe either intentional or just a limitation of the microphone. It can be important to have some roll off with use of a mic on drums to when recording sound directly from a speaker to keep things from getting “muddy” sounding but say for strings/voice/flute it may loose some of the intensity of the sound after the roll off frequency. In the SM-81 graphic above we can also see some high end roll off as well starting with 15,000 Hz. Some microphones will show a positive response enhancement above the “flat” signal. This can be either design intent to enhance the higher frequency reception or a negative as it can make the sound more “tin-ny”. Knowing this you can better pick the mic you need for the job or avoid the wrong microphone.

Sensitivity

I won’t bore you with the specifics of the “technical description” of the ratings of sensitivity only to say the higher the number the better its response to pickup and transmission of the sound to be recorded. Just be sure when reviewing specifications that all manufacturers use the same units of measure in order to do an apple-to-apple comparison.   

Signal to Noise

All electronic devices produce “noise”. The noise can sound like a hiss, hum, or buzz heard in the background, mostly noticeable on silent portions of a recording.

Controlling noise in the recording environment is essential will give you a “clean” sound. The first piece of equipment that can produce noise (and the first to be controlled) is the microphone.

In this case also the higher the signal-to-noise number the better (i.e. higher numbers mean “more signal for less noise”).

For many music genres, such as rock, pop, and blues, there are rarely periods of silence or even low volume. Listen to an FM rock or pop station for a while, and you'll realize that even quiet sections of a song have been boosted to maintain a uniformly high-volume sound. For these genres, the signal to noise ratio for the recording system is not as much of a concern. Most noise in the recording will be buried in the uniformly loud sound.

However, genres like Native American flute as well as classical music and spoken word do have periods of low volume and even silence. A clean recording environment with low noise is critical in these situations.

Hints for Signal to Noise Problems

As mentioned all electronic devices produce some noise and when you have multiple cables connected to multiple devices in the sound path from microphone to the recording device itself you also now have the greater risk of higher noise levels, it is additive.

Here are some hints to decrease noise levels:

  • Do not plug your devices into different power sources the line may have different ground potential (setting up ground faults or loops) and may also have subtle differences in voltage through put.
  • Keep the use of adaptor cables, adaptor connectors, and microphone impedance transformers to a minimum. An example is a microphone transformers used to plug a high impedance three wire XLR microphone and cable into a two wire ¼” low impedance device like an amp or stomp box effects pedal. Each connection is a potential loss of signal and a source of noise. Use the manufacturers recommended cables when at all possible and read the instruction booklets including the spec sheets.
  • Avoid unnecessary repeat signal conversions from analog to digital or digital to analog. Each conversion either way will introduce loss of signal and increased noise. An example might be a digital Synth, which would have a cleaner stronger signal, if interfaced as a Midi device directly to a digital recording device than from the Synth out to an analog amp and then from the amp back to a digital recording device.
  • Use as few signal processors (effects, compressors, exciter/enhancer) as possible to get the sound you want. Each device degrades the signal and introduces noise. 
  • In an analog recording environment, avoid the overuse of bouncing tracks to disk. Each bounce is like making a copy of a copy of a copy and loses something each time. 

Maximum Sound Pressure Level (SPL)

This is a measure measurement in decibels (dB) of the maximum pressure level a sound can make on the microphone before it distortion of the sound. This is less applicable to the flute but very important with drum. Drum produce a percussion wave form that can distort the sound the mic picks up. So if you plan to recording drumming you need to have a mic with a high SPL rating so it will record cleanly. The good news is that one of the more modest priced mics, the SM57 is also very popular for recording drum sets. This dynamic mic also makes a good live performance microphone so it can have use in and out of the studio.

Technical Specifications per manufacturers product information

The boldface entries in this next table indicate the highest performance in a given category/column generally (but not necessarily specific to use with the Native American flute).

Model Frequency Response Roll Off Sensitivity Signal to Noise Max Sound
Pressure
Shure SM57 40 Hz – 15,000 Hz 120 Hz 1.9 mV/Pa N/A 178 dB
Shure SM81 20 Hz – 20,000 Hz 40 Hz 5.6 mV/Pa 78 dBA 136 dB
Sennheiser MD421 II 30 Hz – 17,000 Hz 70-100 Hz 2 mV/Pa N/A 140 dB
AKG C1000s 40 Hz – 20,000 Hz 120 Hz 6 mV/Pa 74 dBA 137 dB
AKG C3000b 20 Hz – 20,000 Hz 55 Hz 25 mV/Pa 80 dBA 140 dB
Audio-Technica AT4050 20 Hz – 20,000 Hz 100 Hz 15.8 mV/Pa 80 dBA 149 dB
Blueberry 22 Hz – 22,000 Hz 40 Hz 21 mV/Pa 68 dBA 133 dB

Visual Characteristics

In our discussion so far, we covered the technical specifications of condenser microphones, commonly referred to as recording microphones. In this section we will examine the actual recorded signals visually for each of the microphones tested. Our purpose was not to make specific recommendations for a particular microphone but to give the player the information needed to make a more informed purchase.

We were also interested in determining if the microphones performed differently with flutes of different octave ranges. As a reminder lets review the methods used in this study. The recordings were made on an all digital recording system using an Apple Mac G3, 500 MHz computer connected to a Mark of the Unicorn 896 analog to digital interface. The recording software was Digital Performer 3.1 DSP system running under OS 9.22. The same phrases were played on each flute using three different keyed flutes a high C# (C#5), and middle F# (F#4), and a low A (A3). The song included long short and expressive notes. Six microphones were used in the testing including AKG C1000s, AKG C3000b, Sennheiser MD421 II, Shure SM81, Audio Technica AT4050, and Blue Blueberry. The microphones were attached to a boom microphone stand the diaphragms focused mid flute at a distance of 1 foot.

Before we review the actual recorded signals lets first primer the visual representation of a recorded sound sample. In the audio flute sample below we see the waveform of a flute recording. The top section shows the entire phrase/song that was recorded. The bottom section is a detailed segment of the entire piece as indicated by the white rectangle in the upper pane. In the lower section the vertical axis represents the amplitude of the signal or strength and weakness. The amplitude is scaled in percent. The waveform mirrors itself above and below the centerline. So the greater the strength of the signal the greater the waveform will extend above and below the mid line. A flat line represents zero signal or silence. 

Waveform diagram

The waveforms are plotted on a horizontal axis against time. This example shows about an 11 second sample. The thickness of a particular individual wave or spike would therefore be the duration of the note played (horizontal) as well as its loudness or softness (vertical).

This particular example also shows another interesting yet undesirable aspect to a recording. In the second waveform cluster to the right in the lower section notice the squared off tops and bottoms to the wave spikes. This is what “clipping” looks like. Clipping occurs when the signal is too “hot” or strong. When this condition occurs the system clips or limits the sound to prevent over saturation and potential system damage. Secondarily the clipped signal when played back will sound distorted. Normally the way to correct this is would be to reduce the input gain or increase the distance of the flute from the microphone. As a reminder we intentionally did not adjust the input gain levels because we wanted to get a technically “apples to apples” comparison of the signals between the microphones regardless if they were either too hot or too cool.

High Flute

Waveform diagramIn the example to the left are the six different signals recorded with the high C# flute. Top to bottom are the

  • AKG C3000b,
  • Shure SM81,
  • Sennheiser MD421 II,
  • Audio Technica AT4050,
  • AKG C1000s, and
  • Blue Blueberry

Visually there are some dramatic differences in the signal strengths of the samples of this flute. The MD421 signal is much too low to give you a good recording without turning up the gain (electronic enhancement of the signal). When you turn up the gain on any device you will also introduce electronic noise levels. This signal would be flat in tonal differences. The SM81 is a 100%+ improvement in recorded signal but it is also fairly weak and would require increased input gain adjustment. The C1000 provided the first adequate signal for a recording. The remaining signals from C3000, AT4050, and Blueberry all yielded strong, well saturated signals, capable of recording the subtly and harmonics of the flute which give it audio presence and interest.

Notice the C3000 signal is close to clipping and the Blueberry had some very minor clipping. The ultimate objective of a recording is to record the strongest signal with the least gain enhancement possible. Adjustments of the waveforms can be adjusted later to give it “color” or apply effects. These effects can include techniques such as, compression, doubling, delay, and reverb. These techniques used correctly give the recorded signals audio spatial presence.


Mid-Range Flute

Waveform diagramThe next section shows the mid ranged F# flute recordings. We can now see that the MD 421 and SM81 signals are still weak and in actuality weaker than in the recordings made with the same microphones using the high C# flute. This gives you a visual picture of a very real issue related to flute size to overall volume.

Smaller flutes not only sound louder - they are louder. The inverse is true of the larger flutes being lower in sound volume. This is not just the proximity phenomenon where the sound of smaller flutes (closer too ears) sound louder than larger flutes (farther away from the ears).

The C1000 signal with this flute is now less adequate. The audio of such a signal might sound weak or “lacking presence”. Subtle expressive play could “wash out” (not be heard well) on play back. This can also be used in a positive way to eliminate flute hiss or breathiness. Again the remaining signals from the other microphones are all well saturated. However the signal of the Blueberry is clipping quite often which would give a poor recording because of distortion.


The good news is too strong a signal can be gain-adjusted down with much less negative effect than with electronically increasing gain. The flute could also be moved further away from the diaphragm of the microphone. Again the primary objective is to record the strongest, purist signal without distortion. So the Blueberry signal could be adjusted but for demonstration purposes was not.


Three Flutes, One Microphone

Waveform diagramAs a way to compare the volume to signal relationship the samples to the right show the high, medium, and low flutes all recorded on the AT-4050 microphone. The first the High C#, second the Medium F#, and lastly the Low A flute. Notice the degree of change in the signal saturation between the top and bottom samples.


Low A Flute

Waveform diagramThe third set of samples is from the Low A flute and as we can see all the waveforms are greatly reduced in signal strength. Although not fully saturated the signals from C3000, AT4050, and Blueberry are the only ones adequate for a “good” quality recording.

Note that none of the samples are clipping. This is further demonstration of the decreased loudness of the lower flutes.

The best signal quality for the low flutes is the C3000 and Blueberry microphones. All of the samples however would require some level of increased gain adjustment for a richer fuller recording.

When recording flutes, especially low flutes, I recommend using two microphones to get a full-recorded signal. One microphone is place at the foot of the flute with the diaphragm pointed up the bore and a second mid bore with the diaphragm pointed down toward the playing holes. This provides for a more balance tone to the recording, as the fundamental and lower notes will record at the same level as the upper holes when played. Otherwise the fundamental will be too great a distance from the diaphragm.


Normalizing the Signal

Waveform diagramSo we now know that the recorded signal can be dependant on microphone sensitivity, proximity of the flute to microphone, key of flute, and number of microphones used. So how can we be assured of good recording in face of these challenges? Well, we now have an arsenal of technology which can be applied to the signal either pre or post recording. On the pre side proper selection of microphone for sensitivity is the first order. Secondly the use of a pre-amp can increase the signal prior to the writing of the signal to disk or tape.

Post recording, one of the more common methods is to normalize the waveforms. This processing analyzes the waveforms and looks at the highest and lowest aspects of the samples. Based on this technology the waveforms are then gain adjusted so all aspects of the waveforms are adjusted accordingly to their original levels.

The screen shot below shows the High C# recordings after being normalized. Notice the dramatic changes to the samples recorded using the MD-421, SM-81, and the AKG C1000 microphones. The others changed but required less gain adjustments overall. Compare them to the un-normalized images in the first graphic. This is just one of the ways to enhance a post recording signal


Subjective Aspects

The final part of this primer we will cover the subjective aspect of microphone selection. The difficulty in doing this is that recording and playing back audio is subject to personal preferences in how the listener like to hear sound. No two people set their home stereo systems exactly the same, not every player likes the same flute maker’s particular sound or voice.

The next comments are based on the way I like to hear sound. There is no good way to pick out a microphone without first listening to them for yourself using the flutes you play, the style of your play, the equipment you use, and as close to the conditions you would be playing in. Try to remain objective in your review and selection process remaining cognizant that you are purchasing a recording microphone not a performance microphone. The recording microphone should give you the hottest signal with the least coloring of the tone.

Given these criteria the SM-81 and MD-421 fall out for selection for use with the Native American flute. This does not in any way mean these are not good recording microphones. An audio engineer will often have a wide selection of microphones to apply to the specific need of the sound to be recorded. The SM-81 is an excellent microphone for use with string instruments such as guitar or piano but as we found was not the best for Native American Flute.

The AKG C1000s had good price/performance and is rugged enough to be used in both live sound reinforcement and home studio use. So if you need multiple microphones for stage and studio and have a limited budget the C1000s might be the best purchase option. Many distributors sell them in a two packs at an even lower price.

The AKG 3000b had a good sensitivity and recording saturation with all flutes used and had a modest street price tag. My personal taste however did not prefer the coloring of the sound the 3000b had on the recorded samples. In my opinion it tended to favor the upper octave notes giving them an un-natural brightness hence the timbre of the flute seemed altered. This was confirmed in the specification graphics that this microphone is engineered to enhance the higher frequency sounds by increasing it sensitivity in that range. This makes it less flat across the recorded range. The sound can be easily adjusted to personal tastes using either pre or post recording technologies.

The AT-4050 did have a flatter response curve, strong signal saturation, and a good flat tonal quality. The price is however much greater than even the 3000b and because of this less affordable to many players. The most costly microphone, the Blue Blueberry gave in my opinion the best performance and recordings. The price tag however makes it the least likely for use by home and project studios except for the most demanding artist or audiophile.

There are many other condenser microphones on the market from makers like AKG, Rode, Shure, Neumann, Audio Technica, Octavia, Blue, Behringer, Sennheiser, and Marshall. The approach I found best was to check major music supply distribution dealers like Musicians Friend , American Musical, or Guitar Center for a wide selection of microphones with general descriptions. Next go directly to the manufacturers websites to get the detailed specification for each microphone. Most sites have this information in PDF format files that can be downloaded and printed for side-by-side comparisons and a listing of dealers near you.

Once you narrow down your choices then take the list to your local dealer along with your flutes and enough time to test the microphones you would like to try properly. I am sure you can find a microphone to fit both your budget and listening preference.

 
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