Audio Systems: Analog aliasing?, analog phone systems, digital telephone systems

Question
QUESTION: Hi:

Is it true that purely-analog audio devices [such as analog cassette, AM radio, and the pre-digital telephone systems*] are immune to aliasing?

*By pre-digital telephone systems, I am referring to how these systems operated prior to using digital technology. Nowadays, many analog phone systems do use DSP somewhere along the line. Similar applies to the analog AM radio, it used to be just analog but now it utilizes some amount of DSP indirectly.

If aliasing is a digital entity that does not affect analog systems, then what is the analog equivalent of aliasing?


Thanks,

Green

ANSWER: Aliasing is present only in the digital domain. If you want an example of what would be considered an undesirable artifact in analog audio, you might expect it from a tape copy of any type which could degrade the signal original signal to the copy (an expected result) causing anything from harmonic, inter modulation distortion and or/ anything but a clean sine wave (square, trapezoidal, etc).

http://en.wikipedia.org/wiki/Aliasing

---------- FOLLOW-UP ----------

QUESTION: So a purely-analog device will not suffer any artifact as a resulting of the high-frequency limit being exceeded?

Let's say one attempts to record a 100 kHz sine-wave tone onto a cassette whose record/playback speed as is slow and the slowest setting on a microcassette recorder? What will be the result? Any distortions?

Answer
The density of magnetic particles on cassette tape along with the tiny magnetic head at best may record 12Khz. Harmonics are rolled off and the -3db point will probably be under 12.5Khz. In the analog world you need a recording to be done on a a lathe or tape that is dense enough to record a frequency of 100Khz. Only laboratory equipment is calibrated to assure that harmonics up to 100Khz can be recorded. In tape not only does the head need to be as large as a Studer S90 but the speed with which it records must be 30ips.

Aliasing does not enter the picture. Distortion will occur mostly due to  a signal too weak or too great. The recording must be done at the optimum bias curve and emergent field, and there are many techniques, such as feedforward, predistortion, postdistortion, EER, LINC, CALLUM, cartesian feedback, etc., in order to avoid the undesired effects of the non-linearities.