Analog vs Digital Mixers
Analog and digital mixers both have their place. It is important to understand the differences when choosing to purchase one or volunteer to work in a venue.
The following 5-minute video compares a Yamaha analog mixer with
a comparable digital mixer, the A&H QU16.
Another good video explaining analog and hybrid mixers is one by GLB Productions.
The image below shows how the controls on an analog mixer compare to those on a digital mixer.
Extra Features of Digital Mixers
As the picture above indicates, a digital mixer has several capabilities that most analog mixers do no have.
Most digital mixers have some type of LCD screen that enables the operator to see the numeric settings for each control as well as a visual representation of its effect on the signal. For example, the EQ curves displayed in the graphic above show the level effect as well as the frequency range affected by each filter. Digital mixers that do not have an LCD screen always have an app that provides this feature on a PC, tablet, or smartphone.
Digital mixers generally have more displays of signal level than a typical analog mixer. For example, the A&H QU32 has a screen that shows the level of most of the inputs and outputs on one screen. One particular display available on many digital mixers is a Real Time Analyzer (RTA). This displays the signal level of several frequencies that make up the signal itself. The number of frequency ranges displayed may differ by mixer. On the A&H QU32, the RTA displays 32 frequency bands. This display is very helpful in setting the EQ, for dealing with feedback, or finding the frequency bands where the sound seems harsh or muted. For an analog mixer, a separate device is required for this feature.
Another important and distinct feature of digital mixers is the ability to save and import specific settings. For example microphone manufacturers makers available EQ settings for several of their microphones which can be imported and saved to a library on the mixer. The manufacturer of the digital mixer may supply a collection of settings that can be used with their mixer. For example the A&H QU32 comes with over 60 library settings. These can be imported and tweaked as needed to meet the specific characteristics of a venue and application. The entire set of control settings on the mixer can be saved in a scene and recalled later as needed. With this feature, a more experienced operator can make settings that inexperienced operators can use, and operators can save the settings they prefer when other people use the mixer from time to time. For theatrical productions, settings can be created and saved for various scenes in the production. None of these options are available on analog mixers.
Digital mixers also have more signal routing options than analog mixers. This provides for more flexible performance monitoring or recording options. Digital mixers also typically support multichannel recording and playback of digital files. All analog mixers have the ability to send a stereo signal to and from a recorder. Some include the ability to digitize the signal for multitrack recording using a USB port. Digital mixers always have some type of sound effects built in, with varying levels of complexity. Some analog mixers include a digital effects component. Digital mixers typically will have the ability to control the levels of a group of channels using what are called DCAs - digitally controlled amplifiers. This improves the ability of the operator to control levels during a live performance or in a recording. For example, a drum kit may employ several microphones. The operator can assign these to a DCA and control the level of the entire drum kit with one fader. In similar fashion, a group of signals can be assigned to a Mute group so that the level of the entire group can be muted as needed.
Most digital mixers can be operated using an app running on a PC, tablet or smartphone. In fact some digital mixers are designed to be operated only in this way, decreasing the size and cost of the mixer itself. The remote device connects to the mixer over a direct ethernet or WiFi connection. Most digital mixers have a digital I/O ports such as USB that allows a computer to be connected for multitrack recording and playback. The mixer can then be used in conjunction with a Digital Audito Workstation.
Physical Size
Another factor to consider is the physical size of the mixer along with its peripherals. An analog mixer with up to 8 or even 20 channels can easily sit on a typical desk or table, but if several other pieces of equipment are needed for effects, compression, or additional EQ, more space or a cabinet will be required. Analog mixers with more than 24 channels can get quite large, and the additional pieces of equipment and their cables can become quite cumbersome. A digital mixer with the same number of channels will be much smaller and may not need any peripherals, as those functions are part of the console but usually require that the operator switch between two or more groups of faders.. Digital mixers with high channel counts usually support some tyle of remote digital I/O box connected with a single cable. This helps reduce the physical size of the mixer itself..
Sound Quality
The sound quality of analog mixers can be quite good these days, with Total Harmonic Distortion below 0.005% over most of the frequency range, Equivalent Noise around -128 dBu, and dynamic range over 100 dB. Even inexpensive digital mixers such as the Behringer XR18 meet these impressive specs, but less expensive analog mixers or those from some less reliable manufacturers may not. The digitization of the analog signal in a mixer is done with a very high sampling frequency, usually 48 kHz or higher. This gives a highly accurate representation of the signal, and the digital signal can be processed with practically zero noise or distortion. Thus, the choice between two good quality mixers depends primarily on cost and operating features, in my opinion. Analog mixers are easier to use, but they lack many capabilities incorporated into digital mixers. If you choose a digital mixer, be prepared for a somewhat steeper learning curve.
Some audio operators who prefer analog mixers like to say that analog sound is "thicker and more natural" than digital sound and claim that they can hear the difference between the two types of reproduction. Similar arguments were used years ago by reviewers of high fidelity equipment and more recently when CDs first came out, saying that CDs could not approach the quality of vinyl records. (It's interesting that today there are some who are giving preference to vinyl over CD or digital audio files.) Some individuals even claimed they could hear the difference between a $5 cable and a similar one costing $100 or more! One needs to be cautious when discussing these topics or examining arguments about them because so many factors come into play, let alone personal bias.
For example, if you play a the same recording on a CD and a vinyl record, you will have no problem distinguishing the vinyl recording because of the hiss, clicks and pops and its more limited dynamic range. You may consider the sound more "natural," but only if you disregard the hiss and pops. Analog tape does not have the pops and clicks of vinyl, but it does have the hiss. You'll hear none of this with a good quality digital recording. Don't get embroiled in the analog vs digital sound debate. You will not be able to hear the difference between a digital mixer and a good analog mixer.
These days, when you encounter a recorded soundtrack, it will almost certainly be digital to some degree. There are a few engineers out there who still prefer analog preamps and some who record directly to vinyl or to high-quality tape, but once recorded, the sound is no longer a perfect representation of the original, because the analog recording medium always introduces some artifacts into the sound. Typically this is noise and a degree of compression due to the physical limitations of the medium or the recording transducer. When an analog signal is driven into distortion, the effects are usually less pronounced than with digital processing, and this is why some engineers prefer analog preamps over digital ones. Most professional recording these days is done using digital workstations that provide more functionality than any analog equipment at less expense. The effects one can add with analog are extremely limited.
So the only time a mixer operator will be dealing with pure analog sound is in a live performance. The moment he decides to record the performance, a digital device will most often be used. Moreover, despite what some purists claim, the operator will not be able to hear the difference in sound between an analog mixer and a digital one. For example, there is no environment that is quiet enough for him to be able to hear the difference between the noise or distortion between the two types of mixers.
However, there is one situation where the analog mixer may have an advantage - when the signal is allowed to overload an amplification stage. When this happens, the distortion produced by an analog stage is significantly less drastic at low levels of overload than with a digital stage of amplification. Thus, when setting up an analog mixer, it is often permissible to allow the peak meters to flash, but a digital mixer is usually set up so that the signal does not ever light the peak meters. On a digital mixer, one can add compression to help ensure that overload does not occur, but on an analog mixer, this may not be an option. Years ago, with analog mixers, one tried to keep sound levels as high as possible within the mixer to maximize the signal/noise ratio. With modern mixers, this is not as critical because of their improved S/N ratios, so one can operate so as to eliminate the possibility of signal overload within the mixer.
Thus, it turns out that some operators who prefer the sound of an analog mixer or prefer an analog (tube) preamp because of its "warmth" may actually have a preference for the slight amount of harmonic distortion created by running the inputs into the "red."
Resources
The links below give some insight into the analog vs digital debate. Some comments don't pertain to mixers, but they provide some technical insight into the differences between the technologies and illustrate the bias that is prevalent in such comparisons.
