Below the Noise Floor — Episode 12: "The AetherSDR Voice Chain, Part One: The Basics"

The AetherSDR transmit voice chain has enough controls to be genuinely overwhelming the first time you open it. This episode cuts through that by starting from zero and walking the signal path from microphone to antenna one stage at a time. Part one of two.

Transcript

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When I first opened the Ether SDR voice controls and looked at everything available: the mic gain, the various meters, the speech processor settings, the equalization, the compression level, the profiles, I closed it and did something else. There were too many knobs and not enough context for what any of them were actually doing. This episode is the episode I needed then. We are going to start from absolute zero and walk through the voice chain one stage at a time, not all at once, not jumping between controls. One stage, what it does, what the meter is telling you at that stage, what good looks like, then the next stage. By the end of this episode, you will have a clean, functional transmitted voice signal. Not a polished, optimized, competition grade signal, that is episode 13. A signal that sounds like a human voice is not distorted and will not cause problems for anyone listening to you. That is the goal here. Functional confidence, not mastery. Let me start by describing what the voice chain actually is, because having a mental map of the whole path makes each individual control easier to understand. Think of the voice chain as a pipe. Audio enters the pipe at one end, your microphone, and exits at the other end as a radio signal coming out of your antenna. Along the way, it passes through several stages, and each stage has controls that affect what the audio looks like when it leaves that stage and enters the next one. If something goes wrong at any stage, every stage after it is also affected. This is why you work through the chain in order, from the microphone end toward the antenna end, rather than randomly adjusting things in the middle. The stages in the Ether SDR transmit voice chain, in order, are the audio input, the mic gain control, the speech processor, the modulator, the power output setting, and the antenna. We are going to go through the first three in this episode, the speech processor and everything after it we will cover in episode 13. Stage 1, the audio input. This is your microphone or whatever audio source you have set as the transmit input in Ether SDR's audio settings. We covered microphone selection back in episode 7, so if you are not sure what device is selected or how to change it, go back and review that episode. For this episode, I am assuming your microphone is connected. Your operating system recognizes it, and EtherSDR is set to use it as the transmit audio input. The first thing to do at this stage, before touching any other control, is to confirm that EtherSDR is actually receiving audio from your microphone. Some software has a transmit audio monitor function that lets you hear your own microphone input through the receive chain. If Ether SDR offers this, enable it now. If not, look for a transmit input level indicator, a meter or bar graph, that responds when you speak. If the meter does not move when you speak, the audio is not getting in, and no amount of adjusting downstream controls will help. Start by solving that problem first, before anything else. Stage 2. Mic gain. Mic gain is the first amplification control in the chain. It takes the raw audio from your microphone and amplifies it to a level that the rest of the chain can work with. Too little mic gain and your signal will be weak and undermodulated, you will be hard to hear even with high power output. Too much mic gain and the audio will clip, distort, before it even reaches the next stage, and no amount of correction downstream can fix distortion that happened here. The mic gain control in Ether SDR is typically a slider or a numerical value. The correct setting is not the highest value available. It is the setting that produces a healthy reading on the transmit input meter without hitting the maximum. Here is how to set mic gain correctly. Put the radio into transmit using the mox button or PTT. You need to be actively transmitting for the transmit meters to respond. Speak into the microphone at your normal operating voice level. The same level you would use in a real contact, a comfortable natural voice, not shouting, not whispering. Watch the transmit input meter. What you want to see, the meter moving actively when you speak, with peaks reaching roughly the upper third of the meter's range, not touching the very top, not bouncing at the top, and occasionally going past it into a red zone, reaching the upper third on normal speech, with occasional peaks from louder syllables getting close to but not exceeding the maximum. What too low looks like, the meter barely moves. Peaks maybe reach the middle of the range. If this is what you see, increase the mic gain. What too high looks like. The meter is consistently at the maximum. Peaks are hitting the top on every syllable. On loud syllables, the meter may be pegged at the limit with no visible variation. If this is what you see, reduce the mic gain. Set the mic gain until peaks are reaching the upper third of the meter on normal speech, then stop. This is your baseline. Everything else in the chain depends on getting this right. One important note on speaking distance and position. The mic gain setting is calibrated for a specific distance between your mouth and the microphone. If you set the gain with the mic two feet away and then move it six inches away during a contact, the level will be too high and you will clip. Find a consistent position for your microphone and use the same position every time. Most operators find that 6 inches to a foot from the microphone is workable for a desk or gooseneck mic, and that a boom mic attached to a headset benefits from being positioned just off to the side of the mouth rather than directly in front to reduce plosive sounds, the burst of air from consonants like P and B. Stage 3. The transmit ALC meter and what it is telling you. Before we get into the speech processor in the next episode, there is another meter in Ether SDR's transmit display that you need to understand. The ALC meter. ALC stands for automatic level control. It is a circuit inside the radio. Not a software control you set, but a feedback mechanism that monitors the transmit signal level and pulls it back if it is getting too high. Think of ALC as the radio protecting itself. If your audio input level is high enough that it would push the transmitter into a distorted region, the ALC kicks in and reduces the transmit power automatically to keep things linear. A small amount of ALC action is normal and expected. A large amount of ALC action, the ALC meter pinned at maximum or consistently reading high, means your audio input is driving the transmitter harder than it should be and the ALC is working hard to compensate. Here is the key thing to understand about ALC. It is not a limiter, it is a compressor, and it has its own time constants and character that can color the audio in unpleasant ways if driven too hard. Heavy ALC action can produce a transmitted voice that sounds squashed, unnatural, or fatiguing to listen to. The goal is not to maximize ALC action, it is to set the chain upstream so ALC barely needs to do anything. After you have set your mic gain correctly in stage 2, watch the ALC meter during normal speech. It should be moving, showing some activity, but not hitting the maximum on every syllable. If the ALC meter is consistently at maximum, your input level is still too high even if the mic gain meter looked acceptable. Reduce the mic gain slightly and recheck. If the ALC meter is barely moving at all with mic gain set correctly, that is fine, it means your input level is conservative, and the transmitter is comfortable. This is not a problem. Now, and this is important, put the radio back into receive before you do anything else. Do not leave it in transmit while you read the rest of this episode. Mox off. Power output in Ether SDR is a setting that determines the maximum RF power the transmitter will produce. It is separate from the audio level chain. Setting high power does not automatically mean the audio is correct. You can have perfectly set audio and low power, or perfectly set audio and high power, or badly set audio, and any power level. The power setting controls how much RF comes out of the radio. The mic gain and ALC discussion above controls whether the audio driving that power output is clean or distorted. For voice operating, set your power output to a level appropriate for the band and contact you are trying to make. We discussed starting at 25 to 50 watts back in episode 7. The power setting in Ether SDR corresponds to what the radio's wattmeter will show during transmission. It does not need to change every time you use the radio. Find a level that works for your antenna and typical operating conditions and leave it there. Here is the chain summary so far, with what good looks like at each stage. Audio input, microphone connected, audio reaching ether SDR, input meter response when you speak. Peaks reaching upper third of transmit input meter on normal speech, not hitting maximum. ALC. Some activity visible, not consistently at maximum during speech. Power output. Set to a level appropriate for your antenna and contacts, not changed frequently. If all four of those are in good shape, you have a transmit signal that is clean at the fundamental level. A clean signal at this baseline is something to be genuinely satisfied with. Most of the problems that new operators run into on their first voice contacts, the bad audio reports, the request to adjust something, the complaints about splatter come from getting one of these four basics wrong. With these right, you are doing better than a significant fraction of operators on the air. Episode 13 takes it from here into the speech processor and equalization, the tools that shape and optimize the audio above the clean baseline. Those controls are genuinely useful, but they are adjustments to something that is already working, not fixes for something that is broken. Get the basics right first. Next episode the Ether SDR Voice Chain, Part 2. EQ, Compression, Vox Refinement, and Profiles for Saving Your Settings. This is below the noise floor.