Qualitative implications of Hot/Cold signal, S/N ratio, Filter sweeps

[Libertine Lush]

Besides an overwhelming amount of questions, there's been a few curiosities I've come across in my entry into this world of recording and technology.

I'm curious to know what, if anything, these things reveal about the quality of the components in an instrument (especially electronic instruments, the ones I'm primarily working with): 1) When someone refers to an instrument's signal as really hot (like the Moog Sub 37) or cold, 2) when there's a fair amount of noise coming from the instrument (like the Volca Keys) when simply plugged in and 3) the significance of how a filter sweep sounds on a synthesizer (besides just being a deeply joyful and beautiful sound)?

My guess is being loud, having little noise and rich filter sweeps speak favorably of the instrument's components, with the last being more subjectively judged.

Thank you.

[RichieWitch]

1) From an engineering perspective, when a signal is "hot", it indicates that the peak-to-peak voltage of the audio signal is too high for the input of the audio device it's being routed to. Where the difference is not too great, this leads to clipping and distortion of the voltage (audio signal). In severe cases, it can damage the audio input.

2) Every audio circuit has a certain amount of "self noise", very low-level audio signals created by the electricity running through the circuitry of the device, unavoidable energy losses, less-than-perfect shielding or grounding, and a whole host of others. If this self noise is great enough to exceed the noise floor of your recording environment, you will see the input meters fluctuating as they measure this (hopefully) low-level audio.

3) Filters are a huge topic. The difference comes from the electrical design of the circuits involved. Diode ladders, transistor ladders, digital filters--there are scores of different circuits that have been devised over the decades, each with a distinctive sound, some of them attributed to famous synths like Moog, Korg's MS-20, the Wasp, the Synthacon, etc. Filters can be described as screaming, wet, creamy, bubbling, buzzing, hollow, and a wild variety of other descriptors. The correct filter is the one that allows you to carve the waveforms of your oscillators into the sound you're looking for. Not all of them would be considered "joyful" or "beautiful", even by those who enjoy a screaming filter.

The "filter sweep" describes the sound created as the frequency cutoff knob is turned to change the portion of the frequency spectrum the filter affects.

How's that?

[Libertine Lush]

Thank you for the wonderfully comprehensive reply!

1) From an engineering perspective, when a signal is "hot", it indicates that the peak-to-peak voltage of the audio signal is too high for the input of the audio device it's being routed to. Where the difference is not too great, this leads to clipping and distortion of the voltage (audio signal). In severe cases, it can damage the audio input.

Perhaps I should be more specific. This is what I've experienced: one synth I have, when plugged into my audio interface, doesn't require gain for the signal to be audible, but another synth does. Does having a quieter output (which I rightly or wrongly conflated with the term "cold signal") mean it has cheaper components?

2) Every audio circuit has a certain amount of "self noise", very low-level audio signals created by the electricity running through the circuitry of the device, unavoidable energy losses, less-than-perfect shielding or grounding, and a whole host of others. If this self noise is great enough to exceed the noise floor of your recording environment, you will see the input meters fluctuating as they measure this (hopefully) low-level audio.

Ah okay. There's a slight buzzing sound from my speakers when simply on; this explains it.

If an instrument produces less noise, does that mean it uses superior parts to one that produces more?

[Libertine Lush]

3)
The "filter sweep" describes the sound created as the frequency cutoff knob is turned to change the portion of the frequency spectrum the filter affects.

Oh, one more thing.

While the difference in filter sweeps from synth to synth is audible to me, is it also supposed to be audible in how it shapes the sound when simply playing notes (without filter sweeps)? I imagine the ability to discern that requires greater familiarity with synthesizers.

When I'm just playing without moving the Filter Cutoff, at this stage, I wouldn't know what filter (Moog Ladder, Curtis, etc) is being used nor would I know what kinds of sounds to look for to try to identify the filter used.

Thanks.

[RichieWitch]

Thank you for the wonderfully comprehensive reply!

You're welcome!

Does having a quieter output (which I rightly or wrongly conflated with the term "cold signal") mean it has cheaper components?

Not necessarily. The output voltage of your synth is determined by the final stage of the output amplifier in that synth. There are two relative standards for line level outputs. -10 db is the standard for consumer electronics; +4 db is the standard for studio gear. However, the two levels have more to do with what the designer thought the gear would be connected to, rather than the quality of the synthesizer itself. Even a cheap line mixer is going to have inputs to accept +4 db line levels, while a hi-fi home theater system costing thousands is going to have -10 db line inputs.

To complicate matters further, back in the 1980's, even pro-level synthesizers had line outputs of -10 db. Most studio line mixers have switches so that you can select the compatible input level. Most mixing boards I've come across expect you'll be using +4 db line inputs.

The two standards are also related to balanced (usually +4 db) vs unbalanced (usually -10 db), but that debate could be a whole forum to itself, and has been on some boards.

Ah okay. There's a slight buzzing sound from my speakers when simply on; this explains it.

Yes.

If an instrument produces less noise, does that mean it uses superior parts to one that produces more?

Generally speaking, yes. If all other factors are equal, the instrument with more self noise has either inferior components or a poorer design. However, take vacuum tubes as an example--sometimes you may be willing to accept more noise to get greater gain. There are design trade-offs that you have to consider when deciding what "inferior" means.

The electronics in vintage Moog and Korg synths were built at a time when semiconductor manufacturing processes were not as precise as they are today. One could argue that the processes were lower in quality. However, an original MS20 costs significantly more than the modern remake. If price follows quality, this would be a contradiction.

[RichieWitch]

While the difference in filter sweeps from synth to synth is audible to me, is it also supposed to be audible in how it shapes the sound when simply playing notes (without filter sweeps)? I imagine the ability to discern that requires greater familiarity with synthesizers.

When I'm just playing without moving the Filter Cutoff, at this stage, I wouldn't know what filter (Moog Ladder, Curtis, etc) is being used nor would I know what kinds of sounds to look for to try to identify the filter used.

You are correct. A discerning ear can tell the type of filter just by listening to audio passing through it, the same way some people can tell you the make and model of a car by hearing its engine.

I run a series of audio tests on all my filters in an attempt to familiarize my ear to each filter's characteristics, which (theoretically) should help me when I'm designing my own sounds and patches. All my hardware synths have inputs that let me run external sounds through the filters, and I have a small Eurorack modular rig that contains a few more filters that I can also introduce into the signal path.

Listening back over my test recordings helps train my ear in the same way that you would train yourself to know the character added by a particular compressor or microphone. It arms you with the knowledge to reach for the sound you hear in your head. You can do the same thing with the oscillators on your synth--not all square waves are created equal.

[Libertine Lush]

I really appreciate all the info you've shared; you've definitively answered these curiosities I've had for while. Thanks so much!

You are correct. A discerning ear can tell the type of filter just by listening to audio passing through it...

I will start listening to my synthesizers anew now. And looking forward to understanding them just a bit better.

[RichieWitch]

Glad I could help!