Designing a simple audio compressor from scratch 

The extra effort here with the animations was definitely appreciated on my end! I love that you slipped a side chain feature in at the very end! Beautiful stuff Mortiz!

I am a hobbyist C++ Audio DSP programmer, so I understand exactly what a compressor does and the functional blocks used to control it, but the actual breakdown of specific implementations using electronic components has always eluded me. Looking at electronic circuits without experience made it difficult to see the "boundaries" between components. Your video has helped me realize that obtaining generalized knowledge of common audio electronics sub-assemblies and the ability to identify those sub-assemblies is the key to my understanding audio electronics in general. I feel significantly less intimidated about designing audio circuits after watching this video. Thank you so much for the work that you do!

Ive taken the full electronics series of courses in my degree track. Stumbling across these videos makes everything I've learned click.

As a pedal designer, compressors have always puzzled me. This is a very nicely done video describing how they work. Thanks

i have been looking for a good compressor circuit that didn't need any fancy components (monolithic VCA chips, OTAs, special FETs , or LDR tuning) for a long time and finally here one is.

You should modify the peak detector to use a precision rectifier instead of a half wave single diode like you use. That way you can reuse the circuit for an envelope detector to control a VCF without noticeable wobble when playing bass frequencies. The big downside to half wave peak detectors like that is that with bass frequencies you tend to hear a lot of wobble in the envelope as it’s only acting on half the peaks.

I just built this circuit with some changes for my guitar. Since unamplified guitar voltages are a few hundred mV at most, I only used one diode on each side of the diode bridge and didn't attenuate the signal going through it. Other than that, I replaced the potentiometers with fixed resistors since I don't have any pots on-hand and changed two or three resistor values, but that's it. It works really great as a compressor.

I have been on the audio scene for over thirty years, I mean on the electronics field rather than in the use of the machines, and believe me...I have never found a book or document that explains in both easy and comprehensive way the subject you have gift us on this video. Not only the practical design and the theory behind (without getting into heavy design issues) but, also, the perfect animation and perfectly chained explanation. I have subscribed immediately to your channel. Thank you for your work.

This is exactly, how to learn analog circuit design. I absolutely love how you describe every single detail. That shows that you truly understand what you are doing, making it really really helpful for others to understand these concepts. So helpful, thank you so much.

2:02 - My god. This is the best explanation of compression I have ever seen

Just paused at 8 minutes to say WOW! The animations! They really help to grasp the flow in a much easier way! Thank you!!! 🙏

This is the best stuff about electrotechnical principles in music. This beats all that I've learned for several years in my engineering university. Just excellent and very inspiring! Thank you!

This single video is more useful than any of my circuits classes ever were

I’m not sure how I haven’t had your videos in my recommended yet but I’m genuinely excited to have found your channel

i've been wanting to learn about signal processing, and electronics in general, for a while, but it all just seemed so confusing. the animations and visualizations in this video were amazing, and helped finally feel like i have a chance at understanding things! thank you so much for this amazing video!

This works great for symmetric wave forms, which is most of the cases. Now, imagine you have a wave form which has negative peaks and no positive peaks, then the peak detector will never turn on. To solve this problem you need to place absolute value circuit before the peak detector, which could be as simple as full wave 4 diode rectifier circuit or its opamp equivalent.

starting the year with incredible stuff! thanks so much for all your effort and great content, you are a truly unique channel in youtube 🔥

Your descriptions are, as always, clear and simple. And I love your animations.

Absolutely beautiful! I love these types of breakdowns!

awesome video! love the animations, they make everything feel much more intuitive

So much dedication on this video. Thank you so much for making it, its so useful and wondrous!!

Thank you Moritz! Great explanation and I really like the animations you made.

absolutely astonishing how well you put together this info.

I love your clear and visually decription - great.

Many audio signals from synths BECOME asymmetrical when they pass through a cap coupled stage. Any pulse wave with a duty cycle less than or greater than 50% will do this. Send a 90% duty cycle pulse wave into the DC coupled input of your scope. It *should* be symmetrical about 0V. Then change to AC coupling. The narrow phase of the pulse have a larger excursion above or below zero than the wide phase. This is due to the time required to charge and discharge the coupling cap. Even some of the example waves in this video show this. Since this is so, if you want your compressor to work well it doesn't make sense to throw away the negative portion of the wave. The negative half could have a significantly larger excursion from zero than the positive half. It's EASY to full-wave rectify the input signal instead. One or two op amps. These kinds of circuits are called precision rectifiers and there are probable a dozen different types available on the internet. That way you get accurate compression of asymmetrical signals.All the famous compressors and limiters derive the side chain from a full wave rectified version of the input not a half wave rectified version. It's so easy to implement it makes no sense to throw away half the signal and wave your hands about audio signals being symmetrical about 0V. We're only talking about $1 worth of parts.

Awesome video! Always super informative and well-explained. Hope you keep making more great videos this year!

Thank you, Moritz, for this outstanding video! It was one of the best that I have seen in a long time! Very comprehensive and comprehensible!! Tempted to get your series of modules just to support you in this effort!!

Beautifully explained, you're a great speaker.

This was a great video! I especially appreciate how you went into your circuit design process, building it up on a breadboard and addressing any hurdles as you came across them. Great work!

Amazing, thank you for bringing this subject to life. Great graphics, animation and as usual clear and deep explanations.

Awesome video. I’ve been really interested in building a compression circuit so this is kind of a godsend. Really great video structure too. Thanks

Very thorough easy to understand explanation, great job

Toller klarer Stil, tolle Videos, danke Mortiz!

Your use of animations is great - it really helps to understand what's going on in the circuit. Nice work!

Animations were very helpful for the explanation! Thanks!

What a great explanation of compression circuits - these videos really helped me whilst studying Audio electronics

Moritz you are great. Thank you for all of your hard work to spread this knowledge!

This is really great! I'm just diving into circuit design, so this was still over my head, but you explain things so well that I started to get it, even though I need to understand the real basics first. I'll definitely be checking out your other content! thanks!

Brilliant walk through and animations! I especially like the step by step explanation and problem solving when the next issue arise. Thanks! 😊✨

sounds pretty good. i think fully rectifying the cv signal would catch initial negative transients that you are missing and improve attack response. that's the only thing i would add

Finally !!! I was hoping you would touch the subject!! Awesome content my friend. My best youtube suggestion video in ages :)

Wow, your educational videos are superior to all others. So elegantly constructed and informative. I thank you.

Appreciate that you shared from the process of designing vs explaining a schematic! This definitely shed some light on a few basic ways compressors can have unique characteristics. Thank you for the hard work!

Genuinely very detailed and well taught. Thank you for showing this. Love the content!

Excellent presentation quality - you must put a lot of time and creative effort into each video. Thanks Moritz!

Been getting into DIY pedals lately, I must say you may be the most concisely informative 'tutor' I've stumbled across. Learned a ton, thanks.

so much knowledge, well taught, with meaningfull explainations and stunning visuals. I learnt a lot. Thank you for this amazing work!

Have been watching this channel from the beginning, these animations are so good at explaining these concepts - this channel is a such a good resource!

This is by far the best explanation I’ve seen on compressors and the building blocks involved. Thanks a bunch!

Best explanation how basic compressor works I ever seen.

This is one of my best electronic related videos that I watched so far. It did give me some inspiration on how to multiply two signals together or how to do frequency modulation.Thanks.

Great description of the functionality. Thanks for the video.

Nice explanation and walk-thru !

circuit using diodes as variable resistors always make me happy and smile. they are always so surprising but work great. thanks!

I've been binging your videos. If only electronics at school was explained how you present it! Thank you so much for your efforts, looking forward to more videos.

This is so elaborate and well explained. Wow. The animations are great too. Thank you!

Loving the diagrams. Gives a really good way to visualize whats going on. Its kind of what my mind see, when looking at a circuit diagram.

As ever, very nice video, accompanying explanation, and pleasingly simple circuit. One needs to distinguish, however, between compression and limiting. Limiters direct the circuit to address the dynamic peaks, while leaving material below the threshold intact. Compressors attempt to achieve an overall average signal level, by limiting peaks in the manner you've illustrated, but also *increasing* gain when content is well below the peak threshold. In practice, the two can sound identical with adjustment of controls, but there can still be audible differences between them when controls are set differently. One of the phenomena compression can result in is often referred to as "breathing". Since analog compressors generally have no means to differentiate between pianissimo signals and background noise. they dramatically increase gain when the input signal is small. If the release/gain-recovery time is long enough, the gradual increase in gain during soft parts results in amplification of background hiss that sounds like someone inhaling - hence "breathing". The cure involves use of as pristine an input signal as one can provide, and as quick a gain-recovery as is plausible. Limiters typically do not encounter breathing. While not strictly true all the time, limiters often involve feed-FORWARD control, while compressors tend to use feed-BACK control. That is, limiters use the input to control the final result, after the gain is applied, while compressors tend to use the amplified result to adjust how the gain is set. That aspect plays a big role in achieving an overall average level-setting in compressors. Another limiter/compressor difference that may not be quite so apparent in the percussion example used in the video is the impact of instrument, or other, signal sources that either sustain or have long decay times. Although we may perceive such sustain or prolonged decay as smooth, it is actually filled with a great many little bumps, often referred to as "envelope ripple". When simple half-wave rectifiers are used to extract information about signal level, that ripple in the resulting control-voltage can produce small rapid fluctuations in output level (or filter-frequency, when used to control a filter) that can sound like "distortion" to the user; especially if used in conjunction with control elements that are able to respond to very quick changes (one of the reasons why photocells are often prized for some forms of sound processing). The solution is often to use better rectification, as well as averaging the detected signal level over a longer period; the goal being to make the control voltage resemble pure DC as much as possible. Again, as elegant as the circuit shown here is - and it IS elegant - it is really predicated on processing short percussive sounds, and would need more to be able to process longer-sustaining sounds without problem.

The animation is great ! Really helps Great videos, as always !

Dude, you are amazing!!!!! You explain and show things just how I like it straight to the point, concise explanation no bullshit. Thank you so much!!!!!

I was just thinking about this! I plan on making my own Eurorack in the new year and my first module is going to be ab envelope follower as it's one of the few things I don't already have on hand, and I realized that ducttaping it to a VCA would be instant compressor! Excited to watch this

I always wanted a video which explains how compressors are engineered and never found one on YT, to this day. Thank you very much! Finally I got some insights.

Thanks for the video! It's a lot simpler than it seems, which explains why this was doable back in the era of vacuum tubes(/valves). Love the animations as well. 👍

Explanations are very good with animations helping people visualise what is going on. Those who are into pro audio side of compressors might like Gyraf Audio diy 4k compressor explanation as it shows pretty simple, typical VCA compressor, explaining how each part works and interacts with others in easy to understand details. Also shows typical balancing circuits, use of IC based parts like THAT VCA's, detectors, etc. Ian Bell of Custom Tube Consoles had or has example of simple opto compressor, i'm not sure it is still there although whole diy part is more than worth checking, same for Gyraf's. I will always be thankful to people like Moritz, Gyrad and Ian Bell, not many take their free time to explain this matters to beginners, or even more advanced pro audio electricians/designers. Many thanks, wish you all the best in 2023.

Brilliant Moritz, this is such a great circuit and beautifully explained as always. The animated visuals are a treat, thanks for all the effort with that - I know it wasn't easy. Looking forward to building this sometime. Happy New Year when it comes :)

The add level of quality was really noticeable with this one. This was a great video.

This why I like the most on the electronics field of knowledge. Amazing channel

Your visualizations are wonderful and these videos help get my head around a lot of EE concepts xD

Best compressor walk-through on Earth!

The Grafiks are amazing. Well done

Wow, great ideas! Compressor is a must to make a nice mix, I've struggled with adding a little bit of soft clipping on a couple of iterations to increase the loudness this way, but that's much more professional sounding!

Animation o_O. It's amazing how well fluid pressure analogy works here. Oscillating membranes are mesmerizing.

Thank you so much for this!! Ive been waiting for this type of video to start making my own comp. Time to get to work!!

So glad I found your channel. Went to school for mechE, this is basically all magic.

Diese Videos sind einfach so informativ wie eine Doppelstunde Physik Leistungskurs, wirklich sehr gute Qualität und man kann einfach alles so leicht verstehen!

Amazing work ! Wanna see more of this in the future ! Keep going man

Wow it's very simple at the same it's very effective good work sir

youre videos are extremely helpful and a major godsend

What a great video. The drawings and animations are fantastic. As an electrical engineer, I've very much enjoyed this.

You sir, by the noticeable loudness difference and perfect clarity of your depth and clarity of your voice, definitely know about compression.

This just helped me so much in understanding compression, thank you!

I just discovered your channel and loved it! Great stuff man please keep up the great work!!

Another great video. Loving the Animations. 🔥 🔥 Luckily my DIY system needs a analog compressor. Happy new year 🎉

That was fabulous, thank you! I especially liked the 'rule of thumb' explanations around some of the feedback mechanisms, and the real-time 'scope traces of control and signal displayed together. The VCA is so simple and I wouldn't have thought of it - I'd be using something more complicated like a FET affecting an op-amp gain stage. In the olden days I think we might even have used a bulb-LDR optocoupler. Very nice work - thank you.

It is unbelivable that i try to make a compressor with sidechaning since last fall (without any succes), and your video is just came to my face and covers everything! This new animations makes a really nice illustration, and as i see you implemet this really well with motion. You are a really kind person to share this knowledge in a professional way. Perfect stuff! Deserve more attention.

Hi Moritz, excellent job. Just a little add on. On every compressor one usually loses some level of the signal, therefore in the output stage you will need one more potentiometer to change the gain of the output stage to recover the original input level.

I am very impressed. The explanations and animations are top notch! Doing just digital circuits for living, that makes me smile 😍 Greets from an hw engineer

I finally understood what a VCA is. Thanks.

This is great and straight forward. There's so many ways to achieve compression that seeing a specific scheme broken down into an actual tutorial with the lab and circuit gives those of us interested an example of a clear pathway for our own designs. Because I am specifically desiring one for guitar ATM, I can see from your circuit a way to incorporate this theory of operation into a feedback path to buck some of my input buffer when the circuit sees an excess. As I understand it, you're demonstrating the implementation of multiple methods of compression for an overall more dynamic circuit and performance. *Anyway, this will definitely help me with the design I have had rolling around in my head.*

I'm amazed that all this can be achieved with a handful of components. Not an Arduino in sight!

I did circuit design and filtering courses at university out of interest, but it never got to the point where I could see those principles being put to use in a real application. This is amazing.

I’m a current EE student with a budding passion for computer music and find this video incredibly inspiring. Thanks for the detailed explanation and impeccable animations!!

Figuring out how to make a sidechaininng compressor has been on my radar of projects i'd like to do and then stumbled across this awesome video! Thank you so much!

more straightforward than I would have thought, I could follow the thought process really well. I expected there to be a catch but it seems somewhat simple, maybe that's from how you explain it :)

Moritz great one! I will add this one to my build list and it gives me some confidence to do it having built your VCA. The side chaining feature is cool in this - I don't know the term but I believe I have heard the effect. I've still got to finalize the breadboard version of your ADSR - still playing with and understanding a bit. Thanks for being a great teacher and resource for the DIY mod community!

This is awesome. The bonus part, sidechain, also explains very well why sidechain filters only affect the control voltage and have no influence on the processed main audio signal. One look at the diagram is enough. Bravo!

DUDE SUPER SLOW CLAP, what and amazing video, i will be sharing this over and over again brother, I love the way you even went in depth on the parts you ended up changing . This just doesn't just show you something , it shows you why you chose to coarse correctly . What an amazing video. I'm so pumped to see your others .

The last time I've heard anything to do with voltages and stuff was at school, yet this is perfectly comprehensible. Might even try it at some point.

I have been looking for a way to make a diy compressor. Thanks Moritz!

This is awesome dude. Subscribed!