Here is a pretty simple chip based audio compressor (expander) too. I used to see complicated designs for recording audio compressor or FM transmitter audio compressor. What the simple one does here? Specially thinking about its quality aspect and working principle. Some chips are now in my hand so.

 

Here is a pretty simple chip based audio compressor (expander) too. I used to see complicated designs for recording audio compressor or FM transmitter audio compressor. What the simple one does here? Specially thinking about its quality aspect and working principle. Some chips are now in my hand so.

Gee, where did you get those old chips?

It is for communication. If you compress the dynamic range of the volume, the PWM of low intensity peaks are increased in intensity and high intensity peaks are decreased in intensity so everything is closer to a 50% duty cycle. Then, once you transmit the dynamic range compressed signal, it can be re-expanded and sounds close to the original.

With standard 10-bit PWM, you end up with a very narrow dynamic range (linear over 10-bits) as applied to the log compression and 10-bits.

You must follow design rules quite strictly or you will get a lot of noise with those chips. A log compression will pick up a lot of noise in general. So, don’t expect perfection on a breadboard.

 

The MC33110 is obsolete and is not made anymore. It was never designed for PWM, it was designed to compress and expand analog audio like the old Philips compander ICs did.
I hate to hear an FM station compress the audio so that the background music level changes with the bass beat of the music.

 

The MC33110 is obsolete and is not made anymore. It was never designed for PWM, it was designed to compress and expand analog audio like the old Philips compander ICs did.
I hate to hear an FM station compress the audio so that the background music level changes with the bass beat of the music.

AG,
What is the reason behind compressing dynamic range, is it just to prevent loss of low amplitude signals during transmission? Or are there other motivations?

I always assumed it would add dynamic range for signals transmitted by some encoding method (PWM, FM, etc) where it can be expanded on the receiving end.

 

Gee, where did you get those old chips?

It is for communication. If you compress the dynamic range of the volume, the PWM of low intensity peaks are increased in intensity and high intensity peaks are decreased in intensity so everything is closer to a 50% duty cycle. Then, once you transmit the dynamic range compressed signal, it can be re-expanded and sounds close to the original.


You must follow design rules quite strictly or you will get a lot of noise with those chips. A log compression will pick up a lot of noise in general. So, don’t expect perfection on a breadboard.

18 months ago, a very nice hobbyist from USA had donated me many of useful parts. I am pretty curious about DIY RF communication. So this might be a useful in some way. You are talking about 10 bits design, then does it need digital control and cannot be used as simple analog circuit?

 

18 months ago, a very nice hobbyist from Mars PA (USA) had donated me many of useful parts. I am pretty curious about DIY RF communication. So this might be a useful in some way. You are talking about 10 bits design, then does it need digital control and cannot be used as simple analog circuit?

It can be used with FM as well.

 

AG,
What is the reason behind compressing dynamic range, is it just to prevent loss of low amplitude signals during transmission? Or are there other motivations?

I always assumed it would add dynamic range for signals transmitted by some encoding method (PWM, FM, etc) where it can be expanded on the receiving end.

When an audio signal is compressed then its average level is increased then this radio station sounds louder than another radio station that does not have compression (but today they all have compression). If the audio level from the signal source varies all over the place (recorded music never does) then compression makes the average volume sound at the same level. A radio station must never over-modulate so a limiter is needed. Very few receivers have an expander because it would never be set correctly and each radio station's compressor would be different. With compression used then the dynamic range is reduced and the background music is wrongly modulated by the loudest sounds.