Presence Frequency
Charlotta Menchaca
The audio spectrum range spans from 20 Hz to 20,000 Hz and can be effectively broken down into seven different frequency bands, with each band having a different impact on the total sound.
Many instruments struggle to enter this frequency range, with the exception of a few bass-heavy instruments, such as the bass guitar which has the lowest achievable pitch of 41 Hz. It is difficult to hear the sub-bass range at low volumes due to the Fletcher Munson curves.
The bass range determines how fat or thin the sound is. The fundamental notes of rhythm are centered on this area. Most bass signals in modern music tracks lie around the 90-200 Hz area. The frequencies around 250 Hz can add a feeling of warmth to the bass without loss of definition.
The midrange determines how prominent an instrument is in the mix. Boosting around 1000 Hz can give instruments a horn-like quality. Excess output at this range can sound tinny and may cause ear fatigue. If boosting in this area, be very cautious, especially on vocals. The ear is particularly sensitive to how the human voice sounds and its frequency coverage.
The high midrange is responsible for the attack on percussive and rhythm instruments. If boosted, this range can add presence. However, too much boost around the 3 kHz range can cause listening fatigue.
Sure, you can use spectrum analysis vst plug-ins to help you out, but this is time-consuming, so you don't want to lean on them too heavily. Sooner or later, you will find out that you can hear sound much better than see it.
Understanding frequency regions is essential in audio mixing because it allows you to identify and isolate specific frequency ranges that may be causing problems, requires enhancement in a mix, or need any kind of treatment.
This is the very lowest frequency band, between 20-60Hz. Many of these frequencies are almost 'felt' rather than heard. Your bass instruments and kick drum should often be represented in this range as this is where they will get their feeling of power. However, it is important that you control what is happening in this range too, as too much emphasis here will make your track sound muddy. This is an especially important consideration when making dance music where a heavy sub is required.
This is the range from 250-500Hz. Most musical instruments are present in this range to a greater or lesser extent, so again, getting the balance between them just right is vital. If you have too much going on in this range it can make instruments sound muffled. Many songs can sound muddy due to excess energy in this region. Not enough energy in the low-mids range will make your music sound thin.
This is the range from 500-2000Hz. Too much energy in 500-1000Hz and your mix can have a 'honking' quality and instruments can take on a horn-like timbre. If there is too much happening between 1-2kHz, the mix can start to sound tinny. If the low mids are over-emphasized in your mix, it can lead to it being tiring to listen to as well.
This is the frequency range that provides clarity and definition to your sounds. It is located between 4-6kHz. If you boost this range it can make mix elements feel closer to the listener. Conversely, if you cut here, it can make things sound more distant and transparent. This is the area to boost if you need more 'crispness' from your snare.
When creating an audio system, whether it is for a house, a car, or an embedded or portable device, there is always a balance between cost, size, and quality. Quality has many contributing factors but one of them is the ability for a system to recreate the whole range of audio frequencies needed. This blog will discuss those frequencies and their various subsets as well as how they impact the design of audio enclosures. It will also shed some light on when the different audio ranges are needed and when they are not in an end application.
A great way to see how a speaker, buzzer, or microphone can reproduce these different frequencies is with the frequency response chart. In general, buzzers carry a narrower frequency range because they are only tasked with outputting an audible tone, whereas speakers offer a wider range to recreate sounds and voice.
When it comes to speakers, buzzers, and other output devices, the y-axis on a frequency response chart is in dB SPL or decibels of Sound Pressure Level (roughly interpreted as loudness). For microphones, as they are detecting instead of producing sound, the y-axis is measuring sensitivity in dB. In the example below, note that the x-axis is frequency (on a logarithmic scale) and since the y-axis is dB SPL, it is known that this chart is for a speaker or other output device. Remember that decibels are also logarithmic, so both the x and y axes are logarithmic.
This chart represents how many dB of SPL will be produced with a constant power input at different frequencies. In this case, the output is rather flat with a sharp drop off below 70 Hz and a shallower drop off above 20 kHz. This means that this audio device, with the same input power, will produce approximately the same sound pressure level between 70 Hz and 20 kHz but will produce significantly less sound pressure level outside of those boundaries.
A smaller speaker can move faster, so it can more accurately produce higher frequencies while reducing unwanted harmonics. Outlined in our blog about designing micro speaker enclosures, a smaller speaker also means a correspondingly smaller enclosure, saving space and cost in materials.
To create the same dB SPL at extremely low frequencies, a larger diaphragm is needed to move sufficient air. This is because of the inherent challenges of moving enough air to match the same perceived dB SPL as higher pitches. On the positive side, the increased weight of a larger diaphragm is not as much of an issue at the lower frequencies where it is moving much slower.
Most objects have a resonant frequency - or a frequency at which an object naturally wants to vibrate. A guitar string, for example, when it is plucked, will vibrate at its resonant frequency. If you were to play the resonant frequency with a speaker near the guitar string, it would start to vibrate and increase in amplitude with time. This same phenomenon occurs with other objects, and in regards to audio, can cause unwanted rattles and buzzing with surrounding objects. Our blog on resonance and resonant frequency covers this topic in greater detail.
When designing an enclosure, you need to ensure that the enclosure itself does not have a natural resonant frequency in the same range as the expected audio output or the speaker itself will have both a non-linear output and unwanted harmonics. At the same time, controlling the resonance of a box, or widening the resonance range, is sometimes sought after, depending on the application.
This trade-off in sensitivity, frequency range, robustness, and SPL range is also true with microphone materials. Microphones can be simple electret or MEMS microphones with sufficient yet limited frequency and sensitivity but with durability, small size, and low power requirements. On the opposite end of the spectrum, ribbon microphones that use a thin metallic ribbon as a diaphragm are renowned for their sensitivity and frequency range. As a trade-off, they are so fragile that they cannot be used for many percussive instruments nor should they be carried without a cover on them, lest the diaphragm tears. CUI Devices does offer both electret condenser and MEMS microphone options with wide operating frequencies that span the entire audio frequency range from 20 to 20,000 Hz.
The trade-offs required for these, in addition to the cost of different materials, varies for different audio ranges. Lower range speakers do not need to worry about the cone weight as much but will need suspensions that are capable of larger amounts of movement.
The type of material used for an enclosure will also affect the resonance and sound absorption. When designing an enclosure, whose primary role is to dampen the out-of-phase rearward generated sound, an engineer will want a material that effectively absorbs the sounds. This is more important with lower frequency sound that is harder to dampen.
It is important to note that very few systems and no individual speaker and enclosure will offer the full range of audio with any level of fidelity. In particular, the extreme frequencies require special speakers and enclosures, but for truly accurate reproductions, there needs to be a balance of speakers at every range that is tuned to create the most linear output.
Second, the majority of applications do not require this level of fidelity and a linear output may not be the desired result. For example, a phone only needs to cover the basic human vocal range and even when doubling or tripling the frequency range to accommodate harmonics, it still falls well short of the 20 Hz to 20 kHz range. Another example would be notification or security applications, which need only a buzz, warble, or screech in a very small frequency range but at various SPLs. For these designs, buzzers or sirens that shift the trade-offs away from frequency range and more toward cost, size, power, and loudness are a good option.
The audio frequency range is a large, though not the only, portion of design and component selection with speakers, buzzers, enclosures, and microphones. A fundamental understanding of this range, what it implies in recording or reproduction applications, and how they are related to the physical limitations and constraints of all audio related equipment will inform the design process. The wide variety of audio components from CUI Devices will provide solutions for many different applications with different frequency ranges.
R2 is being instructed to act as a variable resistor with 11 points to represent each 30 degrees of travel from 0 -10 on the control. Anytime a part of the plot goes below the red line, the feedback is lessened by quite a bit and those frequencies pass the phase inverter more easily. The maroon line on each picture is representing the control being at maximum and a massive amount of the frequency band is passing easily.
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