1. Stereo Encoder Mmc4066e Mmc4047 Software
2. Stereo Encoder Mmc4066e Mmc4047 System

Adaugat in Generale 5 comentarii Mai multe scheme cu: 4047. 4066. codoare stereo Aceasta schema decodor stereo este foarte simpla insa asigura codarea stereo a semnalului audio stereo in limite destul de bune. Desi nu are pretentia de a fi un circuit profesional, acest multiplexor stereo este construit cu 2 circuite integrate MMC4066E si MMC4047 si un tranzistor BC547B.

Software stereo encoder to generate a digital MPX stereo signal for FMradio stations.

About this stereo encoder project

This project makes it possible to use a “normal” soundcardto generate a stereo signal for FM radio transmitters. The stereoencoder is a simple application that runs with Windows XP with servicepack 1 or higher.

The maximum frequency of a MPX stereo signal goes up to 53 kHz.So you need a soundcard that can handle a minimum frequency of53 kHz. Nowadays there are cheap soundcards which have a samplerateof 192 kHz. These soundcards can produce frequencies up to 96 kHz.For a frequency of 96 kHz you will need a minimum samplerate of192 kHz.
Most operating systems can not handle a samplerate of 192 kHz.Windows XP WITH Service pack 1 is the first Windows version whichcan handle this.

Advantages

By using a media player on the same computer, the audio-signalwill be edited fully digital, so there is no loss in qualityproduced by A/D converters.
The stereo signal will be calculated digital, so that a perfectstereo signal will be generated and a good stereo separation willbe reached.

Stereo Encoder Mmc4066e Mmc4047 Software

Disadvantages

Little latency between the input and output signal. (can be controlled manually)

Which soundcard to be used

There are a few soundcards who can handle a samplerate of 192 kHz.Most of them can handle the surround 7.1 system. For this projectI use the Terratec Aureon Space. But the new SoundBlaster soundcardscan probably do this job too. If you have experience with othersoundcards, share it with us and write it in the forum.Of course you can also use the contact form.

Minimum system requirements

Processor: 600MHz
Soundcard: at least a samplerate of 192 kHz.
Operating system: Windows XP with Service Pack 1

Stereo Encoder Mmc4066e Mmc4047 System

How does it work

After the program started up, you see a window like above. Selecta soundcard for the Input and Output device. The same soundcardcan be used as Input and Output device. If you do that, be sureyou configure the record configuration well (the soundcard mustnot 'hear' himself).
Adjust the Buffer size. Try to make the Buffer size as small as possible, to keep the latency low.
Also the pre-emphasis, clipper and 15 kHz low pass filter can be switchedon or off.
The pre-emphasis can be switched between 50 and 75 micro seconds. The European standard uses 50 micro seconds. The American standard uses 75 micro seconds.
The clipper can be used after the pre-emphasis. This will cut the high peaks. Because it works after the pre-emphasis, it will mostly cut the high frequencies so there will be no notable distortion heard. If you use the clipper, my advice is to also use the 15 kHz low pass filter.
The 15 kHz low pass filter will take care that frequencies abovethe 15 kHz will be filtered out. This filter is a 10th order IIRButterworth filter.
Use the clipper and the 15 kHz low cut filter to stay within the Stokke mask.
The amplitude of the 38 kHz signal can be controlled manually,so that an optimal stereo separation can be reached. It’salso possible to use the 38 kHz controller as a stereo widenerby shifting him above the 100%. Using this method, the mono signalwill not be affected.
The Output peak is to watch if the signal will not be distorted.The Output peak shows every second the highest output signal. TheOutput peak can have a maximum of 100%. If it gets over the 100%then the volume of the input signal has to be lowered. Adjust thevolume of the input signal to an average of 90% on the input peak meters.When there is no input signal, the Output peak will still showa peak of 8%. This happens because the 19 kHz pilot tone will alwaysbe on the output.
The Start button explains himself. By pressing this button, the stereo coder will do his job.

Adjust the stereosignal

Connect only 1 output channel from you soundcard to the input of thetransmitter. Do not combine the left and the right channel. Switch on the clipper and the 15 kHz low cut filter. Adjust the volume fromthe input signal so that the Input Peak level meters reaches a average of 90%.Adjust the Master volume and the Wave volume on the mix consolefrom the Output device to maximum. Adjust the input signal of yourtransmitter up to 0 dB.
Try to decrease the buffer size. If you hear drop outs, increase the buffer size.

This program has been tested on a Pentium III 600 MHz. with 192MB internal memory. Operating system Windows XP pro with servicepack 1. For the Input device, I used a SoundBlaster Live Platinumsoundcard and for the Output device a Terratec Aureon Space.

Version history

Forum

If you have any questions or suggestions about the program, pleasevisit the forum.