sigfilter: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/sigfilter - from package: speech-tools

You may install the required package with command apt-get install {package}

Error in other languages:
sigfilter: bevel nie gevind nie
sigfilter: comandă negăsită
sigfilter: comando não encontrado
sigfilter: commande introuvable
sigfilter: command not found
sigfilter: käsku ei ole
sigfilter: không tìm thấy lệnh
sigfilter: komanda nerasta
sigfilter: Kommando nicht gefunden.
sigfilter: kommandot finns inte
sigfilter: komut yok
sigfilter: nie znaleziono polecenia
sigfilter: níor aimsíodh an t-ordú
sigfilter: no se encontró la orden
sigfilter: no s'ha trobat l'ordre
sigfilter: opdracht niet gevonden
sigfilter: parancs nem található
sigfilter: perintah tidak ditemukan
sigfilter: príkaz nenájdený
sigfilter: příkaz nenalezen
sigfilter: команда не найдена
sigfilter: командата не е открита
sigfilter: 命令找不到
sigfilter: コマンドが見つかりません