The Analog Myth—Chorus April 21 2014
What does it really mean to be "analog"? In audio electronics, it means that the electrical signal is an analog of the acoustic pressure. In other words, the electrical signal is continuous in both time and amplitude, just as the acoustic pressure is.
(update, 11/11/2015) For everyone that insists I'm wrong about this, I direct you to review the definition of an analog signal. "Analog" means analogous to another continuous signal. In audio, this means analogous to sound pressure. Once you quantize the signal—in either time or voltage—it is no longer analogous to sound pressure. Get over it. It's just a label.
Unfortunately, this definition is forgotten or ignored when some manufacturers market their so-called "analog" chorus (and some echo) pedals. The majority of these pedals use bucket-brigade delay (BBD) devices, which are discrete-time devices that sample the audio signal at discrete intervals in the time domain. Yes, sampling—like digital.
The difference between discrete-time and digital is that discrete-time is quantized only in time, while digital is quantized in both time and amplitude. So, while discrete-time devices such as BBDs aren't digital, they're not analog either. This also doesn't mean that discrete-time devices are better than digital. To understand why, you have to know how a discrete-time device such as a BBD works. A BBD is a long chain of charge storage elements. Each time the audio signal is sampled, the previously stored charge is passed along to the next charge storage element in the chain. Each time this happens, there is a tiny degradation of the signal. But when this happens thousands of times, this degradation (i.e., noise and distortion) adds up.
On the other hand, modern digital audio processors use 24-bit quantization and have noise and distortion measurements far below that of any BBD. For example, here are some specifications of a widely used BBD device compared to a widely-used audio DSP:
|Signal-to-Noise Ratio (higher is better)||Distortion (lower is better)|
|MN3007 BBD||80 dB||0.5 %|
|FV-1 DSP||94 dB||0.015 %|
So, why are these BBD chorus pedals, using inferior technology, often preferred to DSP-based choruses? It's a result of how the pitch modulation is produced. "Analog" choruses use a fixed delay line with a variable sample rate. Most digital choruses, on the other hand, use a fixed sample rate with a variable delay line. This variable delay line must be interpolated when an output sample is in-between two samples in the delay line. This interpolation can produce distortion if not done carefully.
We use a proprietary processing techniques to minimize distortion and produce a faithful reproduction of the input audio, simply transposed in pitch. This results in a very "analog" sounding chorus, yet quieter and with lower distortion.
So, what's my point? Trust you ears and not some label that says "analog" or "digital". These are just technologies, and it is the way they are implemented that determines if the end result sounds good or bad.