Rangecast FAQ
[FAQ-1067] Adjusting Windows audio input levels


Page Type: SOLUTION


OVERVIEW

The Rangecast audio recording process compresses audio to support a wide dynamic range, but if the levels are too high or low, quality is compromised (and some transmissions may even be discarded). A level control is available in Windows Sound to adjust the input levels from each scanner, and Rangecast provides information about observed levels to help determine when adjustments are needed.


SYMPTOMS

When a transmission is recorded, if the average audio level during the recording is extremely high or low, Rangecast (in the default configuration) discards the transmission. This is to screen out transmissions without content (mic clicks, no audio, etc), and recordings that inadvertently capture unintelligible noise (such as buzzing sounds on frequencies carrying digital data traffic).

If the level of an audio input is extremely high or low, then normal transmissions may fall into these "reject transmission" ranges, resulting in lost content.

If all radios belonging to a cluster (feed site #) are similarly affected (all have a bad audio level configuration), then there may be no reception on Rangecast from channels received by these radios.

If a single radio is affected, then a typical symptom is that, on channels received by that radio (alongside others that are working normally), many transmissions will be received -- but a significant fraction of transmissions will be missing (never appear in Rangecast). The absence of these transmissions may be noticed by apparent discontinuities in the conversation or events on the channel, showing that not everything is being captured.


METHOD

There are three steps to adjusting audio levels:

1) determining the current average audio level

2) determining how much the audio level should be changed (e.g. doubled)

3) changing the audio level by that amount

This is not a process of realtime feedback while adjusting a level (e.g. turning a dial until a needle is in the correct range.) Information about the observed audio level is collected statistically over many transmissions, and in addition to local factors, depends on the quality and type of radio systems that are being received by that scanner. That is why 1/2/3 are distinct phases.

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1) determining the current average audio level

There are two methods available for this step, you may use either method:

a) From the PC desktop: Each sender reports the average observed audio level for transmissions recorded to that point in the hour, on the sender display line titled "Avg Audio" (average audio) field "Vol" (volume). For example, in the sender shown here, the average audio level is 16.




This information is cleared at the start of each hour, so for good statistics, it is recommended to observe this value in the second half of the hour (between :30 and :59) during a time of day when the radio is fairly active.

-or- b) From the status page: Click on "Senders", find the line for a scanner you want to adjust, and click on the IP address (a link in the column by that title). This brings up an informational page about the performance of scanners on that single PC.

Scroll down to the section titled "Sender Metrics". For each scanner on the PC, there will be a table showing performance metrics from that scanner over recent hours.



Review the column titled "Audio". This shows the average audio level observed during each hour. Note that there is considerable variation (in this case, 11 to 19); use common sense to get a sense of the range of these numbers, and perhaps a representative value.


2) determining how much the audio level should be changed

Rangecast performs best when the audio level during individual transmissions is between 5 and 30. In general, if the average is within the range 10-25 there should be good performance.

If the observed levels are outside this range, you can estimate the ratio change that would bring it to normal levels. For example, if the average audio level is 3, then you may want to raise the audio level by 5x (which in theory should raise the average level to approximately 15.) If the observed average level is 8, then you may want to double the level of the audio input.

This is an approximate process, don't worry about finding exact values.


3) changing the audio level by that amount

You can adjust the audio input levels through the Windows Sound user interface.

a) Identify which level control corresponds to this radio

[FAQ-1066] Identifying Windows Sound audio input corresponding to each scanner

The levels of each audio input can be observed and adjusted from the Windows Sound recording tab, but the inputs are not labeled or identified, making it unclear which input in Windows Sound corresponds to which scanner. The Rangecast Configuration screen, when searching for hardware, commands each scanner in turn to produce a loud signal. Observing the Windows Sound recording tab when launching Rangecast Configuration provides a way to identify which Windows Sound input is connected to which physical scanner.




b) Click on that input (usually labeled 'microphone') to bring up controls related to the device.

c) Select the "Levels" tab, and adjust the level by the ratio you determined is desired.



Note: if you calculate that the desired level would be above 100 (maximum), raise to 100 and see if that provides adequate performance. If you lower the level, do not lower all the way to zero (1 is the realistic minimum.)

d) Press 'OK'

e) This step applies to the older style black USB interface boxes. If you know you have an RCX interface, you can skip this step.

If there is a "Custom" tab, select that tab, and see if there is a checked checkbox titled AGC



If AGC is checked, this may significantly raise the observed audio levels, in a way that is not desirable. If the audio level is set to 20 or below, then uncheck AGC and set the audio level to 50. This may not be a final adjustment; let the radio collect transmissions in this configuration for at least an hour, then re-adjust the audio levels if necessary. (In rare cases, AGC is left on intentionally to correct for abnormally low audio levels from the scanner.)


REFERENCE

There are usually several radios connected to a single PC, and it's easy to adjust input levels for all the scanners on a PC at the same time. This is usually recommended, since sometimes problems are serious enough to be noticed on one audio input, while other audio inputs on the same PC have smaller errors that might not raise an alarm.


CITATIONS

SYMPTOM


Rangecast FAQ - ID 1067 - last updated 02 August 2017     Images shown - [block]