In a digital recording system, sound is stored and manipulated as a stream of discrete numbers, each number representing the air pressure at a particular time. Figure 1 shows the components of a digital system. These wires carry the numbers that are the result of the analog to digital conversion. The numbers are in the binary number system in which only two characters are used, 1 and 0.
The circuitry is actually built around switches which are either on or off. The value of a character depends on its place in the number, just as in the familiar decimal system. Here are a few equivalents:. Each digit in a number is called a BIT, so that last number is sixteen bits long in its binary form. If we wrote the second number as , it would be sixteen bits long and have a value of 1. The number of bits in the number has a direct bearing on the fidelity of the signal. Figure 2 illustrates how this works.
The number of possible voltage levels at the output is simply the number of values that may be represented by the largest possible number no "in between" values are allowed. If there were only one bit in the number, the ultimate output would be a pulse wave with a fixed amplitude and more or less the frequency of the input signal.
If there are more bits in the number the waveform is more accurately traced, because each added bit doubles the number of possible values. The distortion is roughly the percentage that the least significant bit represents out of the average value. Distortion in digital systems increases as signal levels decrease, which is the opposite of the behavior of analog systems.
The number of bits in the number also determines the dynamic range. Moving a binary number one space to the left multiplies the value by two just as moving a decimal number one space to the left multiplies the value by ten , so each bit doubles the voltage that may be represented.
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Doubling the voltage increases the power available by 6 dB, so we can see the dynamic range available is about the number of bits times 6 dB. The rate at which the numbers are generated is even more important than the number of bits used. Figure 3. If the sampling rate is lower than the frequency we are trying to capture, entire cycles will be missed, and the decoded result would be too low in frequency and might not resemble the proper waveform at all. This kind of mistake is called aliasing. If the sampling rate were exactly the frequency of the input, the result would be a straight line, because the same spot on the waveform would be measured each time.
This can happen even if the sampling rate is twice the frequency of the input if the input is a sine or similar waveform. The sampling rate must be greater than twice the frequency measured for accurate results. The mathematical statement of this is the Nyquist Theorem.
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This implies that if we are dealing with sound, we should sample at least 40, times per second. The Nyquist rate twice the frequency of interest is the lowest allowable sampling rate. For best results, sampling rates twice or four times this should be used. Your early respnonse would be highly appreciated. Thanks Monika. If I connected my audio recorder to my camera like the first picture would I lose any recording quality if I did this.
No quality is lost as the recorder will still capture the high resolution audio and record it to its memory card. What you are gaining are the use of the recorder's superior microphones and pre-amp over those in the camerai f you decide not to use the higher res file of the recorder to sync with in post. I'm mainly a "one-man" team most days. Is there no way to attach say the zoom recorders to a mic stand, boom pole, or even a tripod to get the recorder closer to the subject when I have to work the camera?
Thanks in advance! Sure ther is. I screw the adapter to the mic stand and the recorder to the adaptaer. Great explainations. I think I understand now more about the problems involved in audio recording. I was wondering if you can suggest how to approach my use-case? My typical use-case if trying to record my daughters singing in a performance.
As a parent, I do not access to the stage area so I typically have to record from a distance so I cannot be close to the source as you recommended but on the other hand there is more than a single source. I would prefer not to carry as little as possible and to remain on a limited budget. Is this too limiting to get improvment on audio quality on my camera recording? I was thinking about purchasing a DR for example and record audio either from my seat or near one of the speakers. Would this be a good solution? Could you suggest a better one?
You may also consider miking your daughter with a wireless lavalier for these performances. Another option, if your daughter's school is using a mixer, is tap into one of the lines out XLR or 3. That way you'd get her vocal mic. I'm not a professional videomaker but I search good image quality and now good-excellent audio too Great idea! I' ll just be using two professional cardioid XLR battery powered mics, for now, and later, a lavalier when I need it.
It seems a step up from the. H4n Pro 4-Channel Handy Recorder. Not really a step-up, but it does sounds like a plan, Jerry.
Digital Sound Recording
There would be no high resolution recording! Please e-mail us all the details of your set-up along with make and model numbers of your camera, microphones, and recorders, and what you will be recording. We will be happy to offer you some guidance to get you pointed in the right direction. I really liked your article, however, I still have a question.
I now have a dual recording system, but I'm having problems synchronizing my audio with the video. I've tried the free trial of Plural Eyes, but I'm having problems with the synchronization. Any help would be welcome. Please send us an e-mail describing your specific issues with synchronizing with Plural Eyes software:.
Sam, This is one of the most lucid descriptions of "how to" for sound I have ever read. Thanks and congratuations. Really helpful article to pass on to my less-versed colleagues.
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Thanks for this clear and informative article. It is of course less stable then a boom mic on a dolly, but also far less expensive. Just be sure to balance and secure the combination safely. This article on audio recording was very informative and easy to understand. Sound recording is often overlooked and adds a professional quality to any producrion.