Selecting A Microphone For Recording The Native American Flute - Part 2

In our first discussion we covered the technical specifications of condenser microphones, commonly referred to as recording microphones. In this report 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. 

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.

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.   

The 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 flute not only sound louder they are louder and 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 has 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.

As 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.

The 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 none of the samples are any longer 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.

So 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

The final part of this primer we will cover the subjective aspect of microphone selection. The difficulty in do this that recording and play 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 will be 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 audio phial.

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 www.musiciansfriend.com, www.americanmuscial.com, or www.guitarcenter.com  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