Introduction for configuring the SDR 1000 for optimum voice transmission.

By John W5GI www.w5gi.com   w5gi@aol.com

So what does optimum voice transmission configuration mean?  Simply stated, it is the selection of the right filter width, internal audio processing features, and external audio equipment to achieve superior results during DX, contest, rag chew, AM, or FM contacts.

Microphone 

The SDR 1000 has an abundance of features which make the task of optimizing voice transmission simple. However, the choice of microphone is the most important step in achieving optimal results.  There are hundreds of microphones to choose from and most will work with the SDR-1000.  I prefer the Heil microphones because they perform exceptionally well, are reasonably priced, and Bob Heil‘s outstanding customer support is legendary.  My personal favorite is the Heil PR40 studio microphone because it has a wide frequency response and only costs about $200.  Wide frequency response is important if you want to optimize performance in all modes.  If, on the other hand, you are simply a casual operator, the Heil HM-10/HC5 may be a better choice for you.  This inexpensive microphone has incredible clarity and will work well in all modes.  If you currently have some other manufacturer’s microphone, don’t be afraid to give it a try. You may have to change the pin connections but do so carefully.  If the microphone is improperly wired, you may create a ground loop which can introduce hum, echoes, and other undesirable artifacts. 

Let’s look at the features available within the SDR 1000 software.

Software Settings 

The main panel has three sets of controls pertaining to audio. The MIC gain should initially be set to 50.  Speak into the mic at a normal level and adjust this setting up or down to achieve a 0 db reading during peaks on the ALC meter.  For initial setup, the Compressor (COMP) and Compander (CPDR) should remain off. 

The next place to look is the Transmit Tab found in the Setup Form. 

Transmit Filters

The transmit filters are the single most important software variables in achieving optimum results. They determine the overall tone of the transmitted audio. 

Note:  the following recommendations are based on the use of a wide response 40-10,000 KHz microphone.  Some microphones, like the Heil HC5 and HC4 cut-off the low and high ends, and introduce a peak at about 2 KHz.  It is very important that you know the response of your microphone, which will make setting the EQ easier.

Rag Chewing - For fully body sound, start with the Low at 100 and the High at 3300.  If you have a deep voice, you might want to set the Low at 200.  A 3200Hz bandwidth is more than sufficient to produce superb sounding audio.  

DX and Contest - Set the Low at 300 and High at 3300.  

AM.  A good starting point is Low at 0, High at 4000. 

FM.  The filter width defaults to 12 KHz. No adjustment is necessary.

Note: The settings above are ideal settings. During crowded band conditions, please consider reducing the bandwidth to minimize interference to stations operating on adjacent frequencies.

Compression 

The SDR 1000 uses audio compression to make quiet sounds louder.  This effectively “squashes” the signal between the loudest and the quietest portion of the audio input, i.e., its dynamic range.  The down-side to compression is that it may amplify some unwanted sounds such as breathing.  More is not necessarily better. A good starting point is the default 3dB.  Rarely will one need to increase compression above 10dB.  If you’re a soft-spoken person, you may consider operating with the compressor on all the time.  If you have a loud voice, you probably will not need any compression unless you’re chasing DX or contesting.  In these cases, use between 5-10dB of compression.  Compression is also very effective on AM.  The choice of microphone will play heavily in the compressor settings. 

Compander 

The compander is used to overcome limited dynamic range in one portion of an audio system.  In amateur radio applications this is typically the high frequency response.  The compander is both a compressor and a high frequency expander. For most applications, the compander should be used by itself; however, the compressor could also be used in conjunction with the compander.  When using both, keep the levels low. An ideal setting for the compander is level 3.  

Compression and Companding 

When using both compression and the compander, set the compressor initially at 3 db and the compander at level 3. There is no easy method of achieving the right settings for your voice/microphone.  Experiment on-the-air to obtain optimum settings.  Lower settings usually result in better overall performance. 

Monitor 

The SDR 1000 is equipped with a software monitor.  It provides an accurate audible indication of how the above settings are affecting tonal quality and clarity.  If you have a second receiver, use it to listen to the actual output of the SDR 1000.  If you have a recorder, record your transmission and listen to the play back. This is a good way to assess your audio settings.  Repeat the process with different settings, if necessary, until you achieve the results you’re looking for. 

Equalization

This feature is the most difficult to setup. In order for the EQ to enhance your audio, you will need to ENABLE it first.  It will help to listen to yourself to get the settings optimized. If your mic is too bassy, you’ll want to reduce (CUT) the low frequencies.  Conversely, if you lack mid range and highs, you’ll want to increase (BOOST) the frequencies from 1.6 upward.  You should try moving the sliders only 1-2dB at a time.  The settings pictured above work well with a typical wide response mic with a heavy low end response; however, these settings will not work with a HC4 or HC5, which normally do not require any equalization.  Note that 160 is cut fully.  There is something about this frequency that degrades audio so most audiophiles cut it heavily.  DXers and contesters may want to use the EQ to CUT all frequencies below 300 Hz. Always experiment, listen to yourself, and get on-the-air help to determine the right settings. The DC block is usually not necessary unless you have a microphone/soundcard that has an exceptionally noisy low end frequency response. 

Summary 

Place matrix here of settings 

Sample Sounds 

Place recordings here; EXPLAIN DIFFERENCES IN GRAPHS 

Advanced Techniques and Tools 

Discuss external PROS AND CONS of audio equipment… 

Professional Sound Card and software used to generate software defined audio. E-MU 1820.  

http://www.emu.com/products/product.asp?category=506&subcategory=492&product=9871  

Microphone Heil PR-40
http://www.heilsound.com/proline/pr-40.htm

Cubase SX Platform  
http://www.steinberg.de/Steinberg/defaultb0e4.html 

Note order of devices 

Microphone modeler…just for fun. The PR 40 is just about as good as any thing on the list; however, if you need to impress your friends, you can use the modeler to select different microphone sounds. 

Noise Gate: used to reduce background noise 

10 band Parametric EQ  

Note settings and particularly the graph 

DeEsser: used to tame high end and prevent tearing

Compressor: used to improve dynamic range and make audio sound louder.

Reverb: used to provide additional clarity and depth to the audio

Six channel mixer-the best $50 piece of equipment in my shack. Used for experimenting, recording and much more. I use two-one for transmitting and another for receiving. 

Too Much? (Which it is!) Consider the following.

Although the above equipment works great-it should for the amount of money it cost, your best buy is a W2IHY EQ Plus (seen below), which will make any radio sound just as good as all the equipment above.

References 

Place references here-books, web sites Heil, Nu9N, W2IHY, Microphone comparisons, Musicians Friend, etc.