Example 3.1: A vocal, recorded with a dynamic microphone.
Example 3.2: The same singer, recorded with a small diaphragm condenser microphone.
Example 3.3: The same singer, recorded with a large diaphragm condenser microphone.
Example 3.4: The same singer, recorded with a tube microphone.
Example 3.5: A kick drum recorded with a single kick mic.
Example 3.6: The same kick drum recorded with the same kick mic and a loudspeaker cone mic.
3.9 PHANTOM POWER
Phantom power is a steady DC current, usually sent by mixers and pre-amps, down the mic cable to power condenser microphones (and other mics requiring power for their head amplifier). Not all phantom power supplies are created equal though! True phantom power is +48 V DC. If a piece of equipment is labeled “phantom power” rather than “+48 V,” it can be an indication that it does not be send the full 48 V – and possibly as little as 12 V or less! Most high quality mics do require the full 48 V to perform close to specification. Some mics can run on these lower voltages, but others will become noisier, and their high frequency response will be impaired.
Not all mixers have phantom power switches on all channels – they might be switchable in groups of four, six, eight, or globally. Phantom power presents no danger to dynamic mics – it can be turned on, and will have no effect on them. As previously discussed, some ribbon mics will be damaged by phantom power, others can tolerate it, and some actually need it – so do double-check! Tube mic power supplies may or may not be damaged by phantom power – so it’s best to check with the manufacturer.
By far the safest thing to do is to not send phantom power to anything that doesn’t actually need it. If your mixer switches phantom in blocks, you may be able to group your mics together in “phantom required” and “phantom not required” blocks.
3.10 PROXIMITY EFFECT
Proximity effect is a boost of low and low-mid frequencies that occurs when a directional microphone is close to a sound source. As a general rule, the more directional the mic is, the more pronounced its proximity effect. This means that bidirectional mics have the most,
hyper-cardioids a little less, cardioids a little less again, and wide cardioids the least. Proximity effect can boost frequencies as high as 400 to 500 Hz, with the amount of boost increasing as the frequency gets lower – the amount of boost usually peaks somewhere between 100 to 200 Hz.
Figure 3.13 contains a frequency response chart that shows the near-field (up close) characteristics of a directional mic, with its associated proximity effect, and the free-field (at a distance) characteristics, which are free of proximity effect.
Radio DJs, many announcers and emcees, and some singers use proximity effect deliber-ately to make themselves sound bigger, beefier, and boomier than they do naturally. Generally however, proximity effect is a bad thing in the context of a busy music mix, and a frequent reason for muddy, confused mixes is low and low-mid frequency congestion. In many record-ing situations, particularly smaller rooms or home/project studios, this frequency congestion quickly becomes a problem because of the predominant and close-up use of cardioid and hyper-cardioid microphones – both of which exhibit proximity effect when used close to a sound source. Backing a singer or instrument off the mic by a few more inches can really reduce proximity effect problems.
Some mics, including hand held vocal mics, are built to mitigate proximity effect. This means that they sound great, and not boomy, a few inches from a sound source – but start sounding thin and tinny if they are too far away. If you do have to work with directional mics very close to sound sources, research their characteristics and apply equalization to undo the proximity effect if necessary.
Proximity Effect @
Example 3.7: A voice recorded accurately, or “flat,” from 45 cm (18 in) away.
Example 3.8: The same voice recorded from 8 cm (3 in) away. Boomy proximity effect can be heard.
Figure 3 .13 The dotted line below 1 KHz represents the flatter low frequency response of a directional mic when it is used in the “free-field” (at a distance of more than a couple of feet). The solid line represents the low frequency boost of proximity effect, when the mic is used in the “near field” (up close).
25 50 100 200 500 IK 2K 5K 10K 20K
f (Hz)
+20
dB+10
0
-10
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level of detail and usefulness of the quoted specification usually corresponds to the type, price, and quality of the mic.
“20 TO 20 KHZ”
Many cheaper mics simply state a range of frequencies. Unfortunately this supplies little useful information. Microphones pick up extreme low and high frequencies less well. This simple specification doesn’t tell us how much less sensitive the mic has become at either extreme.
Yes, the mic may pick up 50 Hz and 15 KHz, but it is probably doing so much less effectively than it picks up 2 KHz – you just don’t know from this uninformative specification.
“20 TO 20 KHZ ±3 dB”
Some mics quote an effective frequency range and a tolerance. This is more useful. It tells us that at 20 Hz and 20 KHz, the mic is 3 dB (“slightly”) less sensitive than its average response between those extremes, and that within the quoted frequency range its sensitivity to a particular frequency could vary by up to 6 dB – it could pick up frequency A 3 dB hotter than average, and it could pick up frequency B 3 dB less well than average. When looking at this type of specification, the smaller the tolerance, the flatter and less colored the mic’s sound is – which can be a good thing. However this still does not tell us where those areas of higher and lower than average sensitivities are.
GENERIC FREQUENCY RESPONSE GRAPHS
Frequency response graphs, such as those found in product literature and manuals, are much more useful. As shown in Figure 3.14, these are plots of frequency (x-axis) against a dB scale of relative sensitivity (y-axis), showing how a mic picks up the entire frequency range of an on-axis sound source. While a flatter mic might pick up a much more accurate picture of a sound, it does not mean it’s necessarily the most suitable or flattering mic for every application.
SERIAL NUMBER SPECIFIC FREQUENCY RESPONSE PLOTS
The electronic components in a microphone are all built to specific tolerances. Tighter toler-ances mean more identical behavior – and that multiple mics of the same model will sound more similar. But the fact of the matter is that multiple mics of the same model and vintages can sound a little, or even quite different, depending upon the tolerances they are built to. So, a generic plot printed in the product manual is not necessarily a completely accurate indication of the performance of the mic in your possession.
More expensive, higher quality microphones often include custom, individual, serial number specific frequency response plots for each mic. For professional recording engineers
this is valuable information. If you are buying multiple mics for stereo or multichannel arrays, then the mics should be closely matched. Matched pairs can be purchased from many manu-facturers. They usually cost a little more than buying two unmatched mics because of the extra testing and analysis required to match up the closest pairs – but for serious stereo pair work, this is money well spent.
3.12 OFF-AXIS RESPONSE
All microphones, regardless of their pick-up pattern, become more directional at higher frequen-cies, and more omnidirectional at lower frequencies. The plots shown earlier only show how a microphone responds to sound coming from directly in front of it, on-axis. In a multi-mic recording situation, or any live sound situation, there is also spill – unintended sound from adjacent sound sources reaching the mic off-axis from the sides or behind. Off-axis, a directional mic is much more sensitive to low frequencies than high frequencies. An omnidirectional mic is slightly less sensitive to high frequencies coming from the sides or behind. This means that off-axis spill can be colored, boomy, or muddy, due to the lack of high frequencies that give the sound intelligibility and clarity. This colored spill causes a cumulative buildup of “mud”
in projects recorded with predominantly cardioid and hyper-cardioid mics.
Fi g u r e 3 .14 Top: A frequency response graph for a low budget microphone. The plot is not “flat.”
It has some peaks in its response where the mic is more sensitive – hyping that particular frequency range. Bottom: A “flat” microphone has a much more even, linear response to all frequencies in its effective pick-up range.
dB Budget M icrophone Frequency Response +20
A major difference between cheaper and more expensive, higher quality mics is the quality of the off-axis pick-up. A higher price point usually correlates to a more linear, better sound-ing off-axis response which produces better soundsound-ing spill – and less mud and mush builds up in a recording because of the spill.
High quality microphones also come with frequency response charts that show the mic’s directional sensitivity at different frequencies, as shown in Figure 3.15. These charts are not serial number specific.
Similar to the pick-up pattern diagrams discussed earlier, 0° represents the mic’s response to on-axis sound coming from directly in front, and the farther away each line is from the center of the crosshairs of the diagram, the more sensitive the mic is to sound coming from that direction. The closer to the center of the crosshairs each line gets, the less sensitive the mic is to sound coming from that direction. Different line styles represent different frequencies.
A frequency’s plot is only shown on half the diagram in order to allow additional frequencies to be shown on the other side – but remember, the mic not only exhibits symmetrical pick-up on the left and right, but also in three dimensions, above, below, and around the mic.